<?xml version="1.0" encoding="UTF-8"?>
<linkbase xmlns="http://www.xbrl.org/2003/linkbase" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xlink="http://www.w3.org/1999/xlink" xsi:schemaLocation="http://www.xbrl.org/2003/linkbase http://www.xbrl.org/2003/xbrl-linkbase-2003-12-31.xsd" xmlns:xbrldt="http://xbrl.org/2005/xbrldt">
  <!-- XBRL Document Created with XML Edge from P3 Data Systems -->
  <arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/all" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#all"/>
  <arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#dimension-default"/>
  <arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#dimension-domain"/>
  <arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/domain-member" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#domain-member"/>
  <arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#hypercube-dimension"/>
  <roleRef roleURI="http://cassinfo.com/role/ConsolidatedStatementsOfShareholdersEquity" xlink:type="simple" xlink:href="cass-20201231.xsd#ConsolidatedStatementsOfShareholdersEquity"/>
  <roleRef roleURI="http://cassinfo.com/role/cass-ebpt" xlink:type="simple" xlink:href="cass-20201231.xsd#cass-ebpt"/>
  <roleRef roleURI="http://cassinfo.com/role/SummaryOfSignificantAccountingPoliciesNarrativeDetails" xlink:type="simple" xlink:href="cass-20201231.xsd#SummaryOfSignificantAccountingPoliciesNarrativeDetails"/>
  <roleRef roleURI="http://cassinfo.com/role/SummaryOfSignificantAccountingPoliciesScheduleOfIllustratesImpactOfAdoptionDetails" xlink:type="simple" xlink:href="cass-20201231.xsd#SummaryOfSignificantAccountingPoliciesScheduleOfIllustratesImpactOfAdoptionDetails"/>
  <roleRef roleURI="http://cassinfo.com/role/cass-crarrsocaard" xlink:type="simple" xlink:href="cass-20201231.xsd#cass-crarrsocaard"/>
  <roleRef roleURI="http://cassinfo.com/role/InvestmentInSecuritiesScheduleOfInvestmentSecuritiesDetails" xlink:type="simple" xlink:href="cass-20201231.xsd#InvestmentInSecuritiesScheduleOfInvestmentSecuritiesDetails"/>
  <roleRef roleURI="http://cassinfo.com/role/cass-iissofvoswuld1" xlink:type="simple" xlink:href="cass-20201231.xsd#cass-iissofvoswuld1"/>
  <roleRef roleURI="http://cassinfo.com/role/cass-lsolcd" xlink:type="simple" xlink:href="cass-20201231.xsd#cass-lsolcd"/>
  <roleRef roleURI="http://cassinfo.com/role/cass-lsoaolblcd" xlink:type="simple" xlink:href="cass-20201231.xsd#cass-lsoaolblcd"/>
  <roleRef roleURI="http://cassinfo.com/role/cass-lsoceolpd" xlink:type="simple" xlink:href="cass-20201231.xsd#cass-lsoceolpd"/>
  <roleRef roleURI="http://cassinfo.com/role/LoansSummaryOfCategoryOfLoansConsideredAsTroubledDebtRestructuringDetails" xlink:type="simple" xlink:href="cass-20201231.xsd#LoansSummaryOfCategoryOfLoansConsideredAsTroubledDebtRestructuringDetails"/>
  <roleRef roleURI="http://cassinfo.com/role/LoansSummaryOfAclByCategoryDetails" xlink:type="simple" xlink:href="cass-20201231.xsd#LoansSummaryOfAclByCategoryDetails"/>
  <roleRef roleURI="http://cassinfo.com/role/LoansSummaryOfAllowanceForLoanLossesDetails" xlink:type="simple" xlink:href="cass-20201231.xsd#LoansSummaryOfAllowanceForLoanLossesDetails"/>
  <roleRef roleURI="http://cassinfo.com/role/cass-paesopaed" xlink:type="simple" xlink:href="cass-20201231.xsd#cass-paesopaed"/>
  <roleRef roleURI="http://cassinfo.com/role/AcquiredIntangibleAssetsNarrativeDetails" xlink:type="simple" xlink:href="cass-20201231.xsd#AcquiredIntangibleAssetsNarrativeDetails"/>
  <roleRef roleURI="http://cassinfo.com/role/cass-aiasoiad" xlink:type="simple" xlink:href="cass-20201231.xsd#cass-aiasoiad"/>
  <roleRef roleURI="http://cassinfo.com/role/UnusedAvailableLinesOfCreditDetails" xlink:type="simple" xlink:href="cass-20201231.xsd#UnusedAvailableLinesOfCreditDetails"/>
  <roleRef roleURI="http://cassinfo.com/role/EmployeeBenefitPlansNarrativeDetails" xlink:type="simple" xlink:href="cass-20201231.xsd#EmployeeBenefitPlansNarrativeDetails"/>
  <roleRef roleURI="http://cassinfo.com/role/cass-ebpsoautdtpbod" xlink:type="simple" xlink:href="cass-20201231.xsd#cass-ebpsoautdtpbod"/>
  <roleRef roleURI="http://cassinfo.com/role/cass-ebpsoppcd" xlink:type="simple" xlink:href="cass-20201231.xsd#cass-ebpsoppcd"/>
  <roleRef roleURI="http://cassinfo.com/role/cass-ebpsoltroroad" xlink:type="simple" xlink:href="cass-20201231.xsd#cass-ebpsoltroroad"/>
  <roleRef roleURI="http://cassinfo.com/role/cass-ebpsotfvmbtoad" xlink:type="simple" xlink:href="cass-20201231.xsd#cass-ebpsotfvmbtoad"/>
  <roleRef roleURI="http://cassinfo.com/role/cass-ebpsotaitspbod" xlink:type="simple" xlink:href="cass-20201231.xsd#cass-ebpsotaitspbod"/>
  <roleRef roleURI="http://cassinfo.com/role/cass-ebpsoautdpbootsd" xlink:type="simple" xlink:href="cass-20201231.xsd#cass-ebpsoautdpbootsd"/>
  <roleRef roleURI="http://cassinfo.com/role/EmployeeBenefitPlansScheduleOfExpectedFutureBenefitsPayableDetails" xlink:type="simple" xlink:href="cass-20201231.xsd#EmployeeBenefitPlansScheduleOfExpectedFutureBenefitsPayableDetails"/>
  <roleRef roleURI="http://cassinfo.com/role/cass-ebpsospcd" xlink:type="simple" xlink:href="cass-20201231.xsd#cass-ebpsospcd"/>
  <roleRef roleURI="http://cassinfo.com/role/cass-ebpsotpaiaocld" xlink:type="simple" xlink:href="cass-20201231.xsd#cass-ebpsotpaiaocld"/>
  <roleRef roleURI="http://cassinfo.com/role/Stock-basedCompensationNarrativeDetails" xlink:type="simple" xlink:href="cass-20201231.xsd#Stock-basedCompensationNarrativeDetails"/>
  <roleRef roleURI="http://cassinfo.com/role/cass-sbcsorsod" xlink:type="simple" xlink:href="cass-20201231.xsd#cass-sbcsorsod"/>
  <roleRef roleURI="http://cassinfo.com/role/cass-sbcsosod" xlink:type="simple" xlink:href="cass-20201231.xsd#cass-sbcsosod"/>
  <roleRef roleURI="http://cassinfo.com/role/DisclosuresAboutFairValueOfFinancialInstrumentsNarrativeDetails" xlink:type="simple" xlink:href="cass-20201231.xsd#DisclosuresAboutFairValueOfFinancialInstrumentsNarrativeDetails"/>
  <roleRef roleURI="http://cassinfo.com/role/DisclosuresAboutFairValueOfFinancialInstrumentsScheduleOfCommitmentsToExtendCreditStandbyLettersOfCreditAndCommercialLettersDetails" xlink:type="simple" xlink:href="cass-20201231.xsd#DisclosuresAboutFairValueOfFinancialInstrumentsScheduleOfCommitmentsToExtendCreditStandbyLettersOfCreditAndCommercialLettersDetails"/>
  <roleRef roleURI="http://cassinfo.com/role/cass-isid1" xlink:type="simple" xlink:href="cass-20201231.xsd#cass-isid1"/>
  <roleRef roleURI="http://cassinfo.com/role/LeasesNarrativeDetails" xlink:type="simple" xlink:href="cass-20201231.xsd#LeasesNarrativeDetails"/>
  <roleRef roleURI="http://cassinfo.com/role/LeasesScheduleOfOperatingLeaseLiabilitiesDetails" xlink:type="simple" xlink:href="cass-20201231.xsd#LeasesScheduleOfOperatingLeaseLiabilitiesDetails"/>
  <roleRef roleURI="http://cassinfo.com/role/cass-cfiopcsocbsd" xlink:type="simple" xlink:href="cass-20201231.xsd#cass-cfiopcsocbsd"/>
  <roleRef roleURI="http://cassinfo.com/role/cass-cfiopcsocsoid" xlink:type="simple" xlink:href="cass-20201231.xsd#cass-cfiopcsocsoid"/>
  <roleRef roleURI="http://cassinfo.com/role/cass-cfiopcsosocfd" xlink:type="simple" xlink:href="cass-20201231.xsd#cass-cfiopcsosocfd"/>
  <definitionLink xlink:type="extended" xlink:role="http://cassinfo.com/role/ConsolidatedStatementsOfShareholdersEquity">
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_StatementLineItems" xlink:label="locator_us-gaap_StatementLineItems"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_StockholdersEquity" xlink:label="locator_us-gaap_StockholdersEquity"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_StatementLineItems" xlink:to="locator_us-gaap_StockholdersEquity" use="optional" priority="0" order="1"/>
    <loc xlink:type="locator" xlink:href="cass-20201231.xsd#cass_CumulativeEffectOfAccountingChangeNetOfTax" xlink:label="locator_cass_CumulativeEffectOfAccountingChangeNetOfTax"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_StatementLineItems" xlink:to="locator_cass_CumulativeEffectOfAccountingChangeNetOfTax" use="optional" priority="0" order="2"/>
    <loc xlink:type="locator" xlink:href="cass-20201231.xsd#cass_StockholdersEquity2" xlink:label="locator_cass_StockholdersEquity2"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_StatementLineItems" xlink:to="locator_cass_StockholdersEquity2" use="optional" priority="0" order="3"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_NetIncomeLoss" xlink:label="locator_us-gaap_NetIncomeLoss"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_StatementLineItems" xlink:to="locator_us-gaap_NetIncomeLoss" use="optional" priority="0" order="4"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DividendsCommonStockCash" xlink:label="locator_us-gaap_DividendsCommonStockCash"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_StatementLineItems" xlink:to="locator_us-gaap_DividendsCommonStockCash" use="optional" priority="0" order="5"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DividendsCommonStock" xlink:label="locator_us-gaap_DividendsCommonStock"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_StatementLineItems" xlink:to="locator_us-gaap_DividendsCommonStock" use="optional" priority="0" order="6"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_StockIssuedDuringPeriodValueShareBasedCompensation" xlink:label="locator_us-gaap_StockIssuedDuringPeriodValueShareBasedCompensation"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_StatementLineItems" xlink:to="locator_us-gaap_StockIssuedDuringPeriodValueShareBasedCompensation" use="optional" priority="0" order="7"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_StockIssuedDuringPeriodValueStockOptionsExercised" xlink:label="locator_us-gaap_StockIssuedDuringPeriodValueStockOptionsExercised"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_StatementLineItems" xlink:to="locator_us-gaap_StockIssuedDuringPeriodValueStockOptionsExercised" use="optional" priority="0" order="8"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue" xlink:label="locator_us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_StatementLineItems" xlink:to="locator_us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue" use="optional" priority="0" order="9"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_StatementTable" xlink:label="locator_us-gaap_StatementTable"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="locator_us-gaap_StatementLineItems" xlink:to="locator_us-gaap_StatementTable" use="optional" priority="0" order="10" xbrldt:contextElement="segment" xbrldt:closed="true"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_StatementEquityComponentsAxis" xlink:label="locator_us-gaap_StatementEquityComponentsAxis"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="locator_us-gaap_StatementTable" xlink:to="locator_us-gaap_StatementEquityComponentsAxis" use="optional" priority="0" order="1"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_EquityComponentDomain" xlink:label="locator_us-gaap_EquityComponentDomain"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="locator_us-gaap_StatementEquityComponentsAxis" xlink:to="locator_us-gaap_EquityComponentDomain" use="optional" priority="0" order="20"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_CommonStockMember" xlink:label="locator_us-gaap_CommonStockMember"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_EquityComponentDomain" xlink:to="locator_us-gaap_CommonStockMember" use="optional" priority="0" order="1"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_AdditionalPaidInCapitalMember" xlink:label="locator_us-gaap_AdditionalPaidInCapitalMember"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_EquityComponentDomain" xlink:to="locator_us-gaap_AdditionalPaidInCapitalMember" use="optional" priority="0" order="11"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_RetainedEarningsMember" xlink:label="locator_us-gaap_RetainedEarningsMember"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_EquityComponentDomain" xlink:to="locator_us-gaap_RetainedEarningsMember" use="optional" priority="0" order="21"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_TreasuryStockMember" xlink:label="locator_us-gaap_TreasuryStockMember"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_EquityComponentDomain" xlink:to="locator_us-gaap_TreasuryStockMember" use="optional" priority="0" order="31"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_AccumulatedOtherComprehensiveIncomeMember" xlink:label="locator_us-gaap_AccumulatedOtherComprehensiveIncomeMember"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_EquityComponentDomain" xlink:to="locator_us-gaap_AccumulatedOtherComprehensiveIncomeMember" use="optional" priority="0" order="41"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_TreasuryStockValueAcquiredCostMethod" xlink:label="locator_us-gaap_TreasuryStockValueAcquiredCostMethod"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_StatementLineItems" xlink:to="locator_us-gaap_TreasuryStockValueAcquiredCostMethod" use="optional" priority="0" order="10"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ProceedsAndExcessTaxBenefitFromSharebasedCompensation" xlink:label="locator_us-gaap_ProceedsAndExcessTaxBenefitFromSharebasedCompensation"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_StatementLineItems" xlink:to="locator_us-gaap_ProceedsAndExcessTaxBenefitFromSharebasedCompensation" use="optional" priority="0" order="11"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_OtherComprehensiveIncomeLossNetOfTax" xlink:label="locator_us-gaap_OtherComprehensiveIncomeLossNetOfTax"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_StatementLineItems" xlink:to="locator_us-gaap_OtherComprehensiveIncomeLossNetOfTax" use="optional" priority="0" order="12"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_OtherComprehensiveIncomeLossNetOfTaxPeriodIncreaseDecreaseAbstract" xlink:label="locator_us-gaap_OtherComprehensiveIncomeLossNetOfTaxPeriodIncreaseDecreaseAbstract"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_StatementLineItems" xlink:to="locator_us-gaap_OtherComprehensiveIncomeLossNetOfTaxPeriodIncreaseDecreaseAbstract" use="optional" priority="0" order="13"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIForSaleOfSecuritiesNetOfTax" xlink:label="locator_us-gaap_OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIForSaleOfSecuritiesNetOfTax"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_OtherComprehensiveIncomeLossNetOfTaxPeriodIncreaseDecreaseAbstract" xlink:to="locator_us-gaap_OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIForSaleOfSecuritiesNetOfTax" use="optional" priority="0" order="14"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_OtherComprehensiveIncomeUnrealizedHoldingGainLossOnSecuritiesArisingDuringPeriodNetOfTax" xlink:label="locator_us-gaap_OtherComprehensiveIncomeUnrealizedHoldingGainLossOnSecuritiesArisingDuringPeriodNetOfTax"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_OtherComprehensiveIncomeLossNetOfTaxPeriodIncreaseDecreaseAbstract" xlink:to="locator_us-gaap_OtherComprehensiveIncomeUnrealizedHoldingGainLossOnSecuritiesArisingDuringPeriodNetOfTax" use="optional" priority="0" order="15"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansAdjustmentNetOfTax" xlink:label="locator_us-gaap_OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansAdjustmentNetOfTax"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_OtherComprehensiveIncomeLossNetOfTaxPeriodIncreaseDecreaseAbstract" xlink:to="locator_us-gaap_OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansAdjustmentNetOfTax" use="optional" priority="0" order="16"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_EquityComponentDomain" xlink:label="locator_us-gaap_EquityComponentDomain_81051589-392f-6e36-464b-f120350dab89_default"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="locator_us-gaap_StatementEquityComponentsAxis" xlink:to="locator_us-gaap_EquityComponentDomain_81051589-392f-6e36-464b-f120350dab89_default" use="optional" priority="0" order="30" xbrldt:contextElement="segment"/>
  </definitionLink>
  <definitionLink xlink:type="extended" xlink:role="http://cassinfo.com/role/cass-ebpt">
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_StatementLineItems" xlink:label="locator_us-gaap_StatementLineItems"/>
    <loc xlink:type="locator" xlink:href="cass-20201231.xsd#cass_ScheduleOfProjectedBenefitObligationAssetsFundedStatusAndAmountsRecognizedTableTextBlock" xlink:label="locator_cass_ScheduleOfProjectedBenefitObligationAssetsFundedStatusAndAmountsRecognizedTableTextBlock"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_StatementLineItems" xlink:to="locator_cass_ScheduleOfProjectedBenefitObligationAssetsFundedStatusAndAmountsRecognizedTableTextBlock" use="optional" priority="0" order="0"/>
    <loc xlink:type="locator" xlink:href="cass-20201231.xsd#cass_DefinedBenefitPlanAssumptionsUsedCalculatingBenefitObligationTableTextBlock" xlink:label="locator_cass_DefinedBenefitPlanAssumptionsUsedCalculatingBenefitObligationTableTextBlock"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_StatementLineItems" xlink:to="locator_cass_DefinedBenefitPlanAssumptionsUsedCalculatingBenefitObligationTableTextBlock" use="optional" priority="0" order="1"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ScheduleOfExpectedBenefitPaymentsTableTextBlock" xlink:label="locator_us-gaap_ScheduleOfExpectedBenefitPaymentsTableTextBlock"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_StatementLineItems" xlink:to="locator_us-gaap_ScheduleOfExpectedBenefitPaymentsTableTextBlock" use="optional" priority="0" order="2"/>
    <loc xlink:type="locator" xlink:href="cass-20201231.xsd#cass_ScheduleOfNetPeriodicPensionCostsTableTextBlock" xlink:label="locator_cass_ScheduleOfNetPeriodicPensionCostsTableTextBlock"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_StatementLineItems" xlink:to="locator_cass_ScheduleOfNetPeriodicPensionCostsTableTextBlock" use="optional" priority="0" order="3"/>
    <loc xlink:type="locator" xlink:href="cass-20201231.xsd#cass_ScheduleOfDefinedBenefitPlanAssumptionsUsedCalculatingNetPeriodicBenefitCostTableTextBlock" xlink:label="locator_cass_ScheduleOfDefinedBenefitPlanAssumptionsUsedCalculatingNetPeriodicBenefitCostTableTextBlock"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_StatementLineItems" xlink:to="locator_cass_ScheduleOfDefinedBenefitPlanAssumptionsUsedCalculatingNetPeriodicBenefitCostTableTextBlock" use="optional" priority="0" order="4"/>
    <loc xlink:type="locator" xlink:href="cass-20201231.xsd#cass_ScheduleOfAssumedLongTermRateOfReturnOnAssetsTableTextBlock" xlink:label="locator_cass_ScheduleOfAssumedLongTermRateOfReturnOnAssetsTableTextBlock"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_StatementLineItems" xlink:to="locator_cass_ScheduleOfAssumedLongTermRateOfReturnOnAssetsTableTextBlock" use="optional" priority="0" order="5"/>
    <loc xlink:type="locator" xlink:href="cass-20201231.xsd#cass_ScheduleOfFairValueOfPlanAssetsByTypeOfAssetsTableTextBlock" xlink:label="locator_cass_ScheduleOfFairValueOfPlanAssetsByTypeOfAssetsTableTextBlock"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_StatementLineItems" xlink:to="locator_cass_ScheduleOfFairValueOfPlanAssetsByTypeOfAssetsTableTextBlock" use="optional" priority="0" order="6"/>
    <loc xlink:type="locator" xlink:href="cass-20201231.xsd#cass_ScheduleOfProjectedBenefitObligationFundedStatusAndAmountsRecognizedTableTextBlock" xlink:label="locator_cass_ScheduleOfProjectedBenefitObligationFundedStatusAndAmountsRecognizedTableTextBlock"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_StatementLineItems" xlink:to="locator_cass_ScheduleOfProjectedBenefitObligationFundedStatusAndAmountsRecognizedTableTextBlock" use="optional" priority="0" order="7"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ScheduleOfNetBenefitCostsTableTextBlock" xlink:label="locator_us-gaap_ScheduleOfNetBenefitCostsTableTextBlock"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_StatementLineItems" xlink:to="locator_us-gaap_ScheduleOfNetBenefitCostsTableTextBlock" use="optional" priority="0" order="8"/>
    <loc xlink:type="locator" xlink:href="cass-20201231.xsd#cass_ScheduleOfDefinedBenefitPlanAccumulatedOtherComprehensiveIncomeLossPretaxTableTextBlock" xlink:label="locator_cass_ScheduleOfDefinedBenefitPlanAccumulatedOtherComprehensiveIncomeLossPretaxTableTextBlock"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_StatementLineItems" xlink:to="locator_cass_ScheduleOfDefinedBenefitPlanAccumulatedOtherComprehensiveIncomeLossPretaxTableTextBlock" use="optional" priority="0" order="9"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_StatementTable" xlink:label="locator_us-gaap_StatementTable"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="locator_us-gaap_StatementLineItems" xlink:to="locator_us-gaap_StatementTable" use="optional" priority="0" order="10" xbrldt:contextElement="segment" xbrldt:closed="true"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_RetirementPlanTypeAxis" xlink:label="locator_us-gaap_RetirementPlanTypeAxis"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="locator_us-gaap_StatementTable" xlink:to="locator_us-gaap_RetirementPlanTypeAxis" use="optional" priority="0" order="1"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_RetirementPlanTypeDomain" xlink:label="locator_us-gaap_RetirementPlanTypeDomain"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="locator_us-gaap_RetirementPlanTypeAxis" xlink:to="locator_us-gaap_RetirementPlanTypeDomain" use="optional" priority="0" order="20"/>
    <loc xlink:type="locator" xlink:href="cass-20201231.xsd#cass_SupplementalExecutiveRetirementPlanMember" xlink:label="locator_cass_SupplementalExecutiveRetirementPlanMember"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_RetirementPlanTypeDomain" xlink:to="locator_cass_SupplementalExecutiveRetirementPlanMember" use="optional" priority="0" order="11"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_RetirementPlanTypeDomain" xlink:label="locator_us-gaap_RetirementPlanTypeDomain_6ebcdfaa-5063-946a-dab7-3b3298015b56_default"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="locator_us-gaap_RetirementPlanTypeAxis" xlink:to="locator_us-gaap_RetirementPlanTypeDomain_6ebcdfaa-5063-946a-dab7-3b3298015b56_default" use="optional" priority="0" order="30" xbrldt:contextElement="segment"/>
  </definitionLink>
  <definitionLink xlink:type="extended" xlink:role="http://cassinfo.com/role/SummaryOfSignificantAccountingPoliciesNarrativeDetails">
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_StatementLineItems" xlink:label="locator_us-gaap_StatementLineItems"/>
    <loc xlink:type="locator" xlink:href="cass-20201231.xsd#cass_PercentageHoldingRequiredToAccountInvestmentsNonMarketableEquityInvestments" xlink:label="locator_cass_PercentageHoldingRequiredToAccountInvestmentsNonMarketableEquityInvestments"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_StatementLineItems" xlink:to="locator_cass_PercentageHoldingRequiredToAccountInvestmentsNonMarketableEquityInvestments" use="optional" priority="0" order="0"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_PropertyPlantAndEquipmentUsefulLife" xlink:label="locator_us-gaap_PropertyPlantAndEquipmentUsefulLife"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_StatementLineItems" xlink:to="locator_us-gaap_PropertyPlantAndEquipmentUsefulLife" use="optional" priority="0" order="1"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_PreferredStockDividendRatePercentage" xlink:label="locator_us-gaap_PreferredStockDividendRatePercentage"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_StatementLineItems" xlink:to="locator_us-gaap_PreferredStockDividendRatePercentage" use="optional" priority="0" order="2"/>
    <loc xlink:type="locator" xlink:href="cass-20201231.xsd#cass_AssetsAndLiabilitiesExpectedToBeAddedToBalanceSheetFromAdoptionOfASU" xlink:label="locator_cass_AssetsAndLiabilitiesExpectedToBeAddedToBalanceSheetFromAdoptionOfASU"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_StatementLineItems" xlink:to="locator_cass_AssetsAndLiabilitiesExpectedToBeAddedToBalanceSheetFromAdoptionOfASU" use="optional" priority="0" order="3"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_StatementTable" xlink:label="locator_us-gaap_StatementTable"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="locator_us-gaap_StatementLineItems" xlink:to="locator_us-gaap_StatementTable" use="optional" priority="0" order="10" xbrldt:contextElement="segment" xbrldt:closed="true"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_PropertyPlantAndEquipmentByTypeAxis" xlink:label="locator_us-gaap_PropertyPlantAndEquipmentByTypeAxis"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="locator_us-gaap_StatementTable" xlink:to="locator_us-gaap_PropertyPlantAndEquipmentByTypeAxis" use="optional" priority="0" order="1"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_PropertyPlantAndEquipmentTypeDomain" xlink:label="locator_us-gaap_PropertyPlantAndEquipmentTypeDomain"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="locator_us-gaap_PropertyPlantAndEquipmentByTypeAxis" xlink:to="locator_us-gaap_PropertyPlantAndEquipmentTypeDomain" use="optional" priority="0" order="20"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_BuildingMember" xlink:label="locator_us-gaap_BuildingMember"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_PropertyPlantAndEquipmentTypeDomain" xlink:to="locator_us-gaap_BuildingMember" use="optional" priority="0" order="1"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_LeaseholdImprovementsMember" xlink:label="locator_us-gaap_LeaseholdImprovementsMember"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_PropertyPlantAndEquipmentTypeDomain" xlink:to="locator_us-gaap_LeaseholdImprovementsMember" use="optional" priority="0" order="11"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_PropertyPlantAndEquipmentOtherTypesMember" xlink:label="locator_us-gaap_PropertyPlantAndEquipmentOtherTypesMember"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_PropertyPlantAndEquipmentTypeDomain" xlink:to="locator_us-gaap_PropertyPlantAndEquipmentOtherTypesMember" use="optional" priority="0" order="21"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/srt/2020/elts/srt-2020-01-31.xsd#srt_RangeAxis" xlink:label="locator_srt_RangeAxis"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="locator_us-gaap_StatementTable" xlink:to="locator_srt_RangeAxis" use="optional" priority="0" order="2"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/srt/2020/elts/srt-2020-01-31.xsd#srt_RangeMember" xlink:label="locator_srt_RangeMember"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="locator_srt_RangeAxis" xlink:to="locator_srt_RangeMember" use="optional" priority="0" order="20"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/srt/2020/elts/srt-2020-01-31.xsd#srt_MaximumMember" xlink:label="locator_srt_MaximumMember"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_srt_RangeMember" xlink:to="locator_srt_MaximumMember" use="optional" priority="0" order="2"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/srt/2020/elts/srt-2020-01-31.xsd#srt_MinimumMember" xlink:label="locator_srt_MinimumMember"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_srt_RangeMember" xlink:to="locator_srt_MinimumMember" use="optional" priority="0" order="12"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_PropertyPlantAndEquipmentTypeDomain" xlink:label="locator_us-gaap_PropertyPlantAndEquipmentTypeDomain_3cbfa82c-829a-59de-59b1-70e04d3b24fd_default"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="locator_us-gaap_PropertyPlantAndEquipmentByTypeAxis" xlink:to="locator_us-gaap_PropertyPlantAndEquipmentTypeDomain_3cbfa82c-829a-59de-59b1-70e04d3b24fd_default" use="optional" priority="0" order="30" xbrldt:contextElement="segment"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/srt/2020/elts/srt-2020-01-31.xsd#srt_RangeMember" xlink:label="locator_srt_RangeMember_4b0e09f0-63f9-71ef-7ab8-e29ce19062cf_default"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="locator_srt_RangeAxis" xlink:to="locator_srt_RangeMember_4b0e09f0-63f9-71ef-7ab8-e29ce19062cf_default" use="optional" priority="0" order="30" xbrldt:contextElement="segment"/>
  </definitionLink>
  <definitionLink xlink:type="extended" xlink:role="http://cassinfo.com/role/SummaryOfSignificantAccountingPoliciesScheduleOfIllustratesImpactOfAdoptionDetails">
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_StatementLineItems" xlink:label="locator_us-gaap_StatementLineItems"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_AssetsAbstract" xlink:label="locator_us-gaap_AssetsAbstract"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_StatementLineItems" xlink:to="locator_us-gaap_AssetsAbstract" use="optional" priority="0" order="0"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_LoansAndLeasesReceivableAllowance" xlink:label="locator_us-gaap_LoansAndLeasesReceivableAllowance"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_AssetsAbstract" xlink:to="locator_us-gaap_LoansAndLeasesReceivableAllowance" use="optional" priority="0" order="1"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DeferredTaxAssetsValuationAllowance" xlink:label="locator_us-gaap_DeferredTaxAssetsValuationAllowance"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_AssetsAbstract" xlink:to="locator_us-gaap_DeferredTaxAssetsValuationAllowance" use="optional" priority="0" order="2"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_LiabilitiesAbstract" xlink:label="locator_us-gaap_LiabilitiesAbstract"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_StatementLineItems" xlink:to="locator_us-gaap_LiabilitiesAbstract" use="optional" priority="0" order="3"/>
    <loc xlink:type="locator" xlink:href="cass-20201231.xsd#cass_ReserveForUnfundedCommitments" xlink:label="locator_cass_ReserveForUnfundedCommitments"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_LiabilitiesAbstract" xlink:to="locator_cass_ReserveForUnfundedCommitments" use="optional" priority="0" order="4"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_StockholdersEquityAbstract" xlink:label="locator_us-gaap_StockholdersEquityAbstract"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_StatementLineItems" xlink:to="locator_us-gaap_StockholdersEquityAbstract" use="optional" priority="0" order="5"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_RetainedEarningsAccumulatedDeficit" xlink:label="locator_us-gaap_RetainedEarningsAccumulatedDeficit"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_StockholdersEquityAbstract" xlink:to="locator_us-gaap_RetainedEarningsAccumulatedDeficit" use="optional" priority="0" order="6"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_StatementTable" xlink:label="locator_us-gaap_StatementTable"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="locator_us-gaap_StatementLineItems" xlink:to="locator_us-gaap_StatementTable" use="optional" priority="0" order="10" xbrldt:contextElement="segment" xbrldt:closed="true"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/srt/2020/elts/srt-2020-01-31.xsd#srt_RestatementAxis" xlink:label="locator_srt_RestatementAxis"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="locator_us-gaap_StatementTable" xlink:to="locator_srt_RestatementAxis" use="optional" priority="0" order="1"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/srt/2020/elts/srt-2020-01-31.xsd#srt_RestatementDomain" xlink:label="locator_srt_RestatementDomain"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="locator_srt_RestatementAxis" xlink:to="locator_srt_RestatementDomain" use="optional" priority="0" order="20"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/srt/2020/elts/srt-2020-01-31.xsd#srt_ScenarioPreviouslyReportedMember" xlink:label="locator_srt_ScenarioPreviouslyReportedMember"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_srt_RestatementDomain" xlink:to="locator_srt_ScenarioPreviouslyReportedMember" use="optional" priority="0" order="11"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/srt/2020/elts/srt-2020-01-31.xsd#srt_RestatementAdjustmentMember" xlink:label="locator_srt_RestatementAdjustmentMember"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_srt_RestatementDomain" xlink:to="locator_srt_RestatementAdjustmentMember" use="optional" priority="0" order="21"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/srt/2020/elts/srt-2020-01-31.xsd#srt_RestatementDomain" xlink:label="locator_srt_RestatementDomain_d6ec40e7-389f-5643-56db-874ced5b3e65_default"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="locator_srt_RestatementAxis" xlink:to="locator_srt_RestatementDomain_d6ec40e7-389f-5643-56db-874ced5b3e65_default" use="optional" priority="0" order="30" xbrldt:contextElement="segment"/>
  </definitionLink>
  <definitionLink xlink:type="extended" xlink:role="http://cassinfo.com/role/cass-crarrsocaard">
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ComplianceWithRegulatoryCapitalRequirementsUnderBankingRegulationsLineItems" xlink:label="locator_us-gaap_ComplianceWithRegulatoryCapitalRequirementsUnderBankingRegulationsLineItems"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_Capital" xlink:label="locator_us-gaap_Capital"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_ComplianceWithRegulatoryCapitalRequirementsUnderBankingRegulationsLineItems" xlink:to="locator_us-gaap_Capital" use="optional" priority="0" order="0"/>
    <loc xlink:type="locator" xlink:href="cass-20201231.xsd#cass_CommonEquityTierOneRiskBasedCapital" xlink:label="locator_cass_CommonEquityTierOneRiskBasedCapital"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_ComplianceWithRegulatoryCapitalRequirementsUnderBankingRegulationsLineItems" xlink:to="locator_cass_CommonEquityTierOneRiskBasedCapital" use="optional" priority="0" order="1"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_TierOneRiskBasedCapital" xlink:label="locator_us-gaap_TierOneRiskBasedCapital"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_ComplianceWithRegulatoryCapitalRequirementsUnderBankingRegulationsLineItems" xlink:to="locator_us-gaap_TierOneRiskBasedCapital" use="optional" priority="0" order="2"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_TierOneLeverageCapital" xlink:label="locator_us-gaap_TierOneLeverageCapital"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_ComplianceWithRegulatoryCapitalRequirementsUnderBankingRegulationsLineItems" xlink:to="locator_us-gaap_TierOneLeverageCapital" use="optional" priority="0" order="3"/>
    <loc xlink:type="locator" xlink:href="cass-20201231.xsd#cass_CapitalToRiskWeightedAssets1" xlink:label="locator_cass_CapitalToRiskWeightedAssets1"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_ComplianceWithRegulatoryCapitalRequirementsUnderBankingRegulationsLineItems" xlink:to="locator_cass_CapitalToRiskWeightedAssets1" use="optional" priority="0" order="4"/>
    <loc xlink:type="locator" xlink:href="cass-20201231.xsd#cass_CommonEquityTierOneRiskBasedCapitalToRiskWeightedAssets" xlink:label="locator_cass_CommonEquityTierOneRiskBasedCapitalToRiskWeightedAssets"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_ComplianceWithRegulatoryCapitalRequirementsUnderBankingRegulationsLineItems" xlink:to="locator_cass_CommonEquityTierOneRiskBasedCapitalToRiskWeightedAssets" use="optional" priority="0" order="5"/>
    <loc xlink:type="locator" xlink:href="cass-20201231.xsd#cass_TierOneRiskBasedCapitalToRiskWeightedAssets1" xlink:label="locator_cass_TierOneRiskBasedCapitalToRiskWeightedAssets1"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_ComplianceWithRegulatoryCapitalRequirementsUnderBankingRegulationsLineItems" xlink:to="locator_cass_TierOneRiskBasedCapitalToRiskWeightedAssets1" use="optional" priority="0" order="6"/>
    <loc xlink:type="locator" xlink:href="cass-20201231.xsd#cass_TierOneLeverageCapitalToAverageAssets1" xlink:label="locator_cass_TierOneLeverageCapitalToAverageAssets1"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_ComplianceWithRegulatoryCapitalRequirementsUnderBankingRegulationsLineItems" xlink:to="locator_cass_TierOneLeverageCapitalToAverageAssets1" use="optional" priority="0" order="7"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_CapitalRequiredForCapitalAdequacy" xlink:label="locator_us-gaap_CapitalRequiredForCapitalAdequacy"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_ComplianceWithRegulatoryCapitalRequirementsUnderBankingRegulationsLineItems" xlink:to="locator_us-gaap_CapitalRequiredForCapitalAdequacy" use="optional" priority="0" order="8"/>
    <loc xlink:type="locator" xlink:href="cass-20201231.xsd#cass_CommonEquityTierOneRiskBasedCapitalRequiredForCapitalAdequacy" xlink:label="locator_cass_CommonEquityTierOneRiskBasedCapitalRequiredForCapitalAdequacy"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_ComplianceWithRegulatoryCapitalRequirementsUnderBankingRegulationsLineItems" xlink:to="locator_cass_CommonEquityTierOneRiskBasedCapitalRequiredForCapitalAdequacy" use="optional" priority="0" order="9"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ScheduleOfComplianceWithRegulatoryCapitalRequirementsUnderBankingRegulationsTable" xlink:label="locator_us-gaap_ScheduleOfComplianceWithRegulatoryCapitalRequirementsUnderBankingRegulationsTable"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="locator_us-gaap_ComplianceWithRegulatoryCapitalRequirementsUnderBankingRegulationsLineItems" xlink:to="locator_us-gaap_ScheduleOfComplianceWithRegulatoryCapitalRequirementsUnderBankingRegulationsTable" use="optional" priority="0" order="10" xbrldt:contextElement="segment" xbrldt:closed="true"/>
    <loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/dei/2020/dei-2020-01-31.xsd#dei_LegalEntityAxis" xlink:label="locator_dei_LegalEntityAxis"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="locator_us-gaap_ScheduleOfComplianceWithRegulatoryCapitalRequirementsUnderBankingRegulationsTable" xlink:to="locator_dei_LegalEntityAxis" use="optional" priority="0" order="1"/>
    <loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/dei/2020/dei-2020-01-31.xsd#dei_EntityDomain" xlink:label="locator_dei_EntityDomain"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="locator_dei_LegalEntityAxis" xlink:to="locator_dei_EntityDomain" use="optional" priority="0" order="20"/>
    <loc xlink:type="locator" xlink:href="cass-20201231.xsd#cass_CassInformationSystemsIncMember" xlink:label="locator_cass_CassInformationSystemsIncMember"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_dei_EntityDomain" xlink:to="locator_cass_CassInformationSystemsIncMember" use="optional" priority="0" order="1"/>
    <loc xlink:type="locator" xlink:href="cass-20201231.xsd#cass_CassCommercialBankMember" xlink:label="locator_cass_CassCommercialBankMember"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_dei_EntityDomain" xlink:to="locator_cass_CassCommercialBankMember" use="optional" priority="0" order="11"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_TierOneRiskBasedCapitalRequiredForCapitalAdequacy" xlink:label="locator_us-gaap_TierOneRiskBasedCapitalRequiredForCapitalAdequacy"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_ComplianceWithRegulatoryCapitalRequirementsUnderBankingRegulationsLineItems" xlink:to="locator_us-gaap_TierOneRiskBasedCapitalRequiredForCapitalAdequacy" use="optional" priority="0" order="10"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_TierOneLeverageCapitalRequiredForCapitalAdequacy" xlink:label="locator_us-gaap_TierOneLeverageCapitalRequiredForCapitalAdequacy"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_ComplianceWithRegulatoryCapitalRequirementsUnderBankingRegulationsLineItems" xlink:to="locator_us-gaap_TierOneLeverageCapitalRequiredForCapitalAdequacy" use="optional" priority="0" order="11"/>
    <loc xlink:type="locator" xlink:href="cass-20201231.xsd#cass_CapitalRequiredForCapitalAdequacyToRiskWeightedAssets1" xlink:label="locator_cass_CapitalRequiredForCapitalAdequacyToRiskWeightedAssets1"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_ComplianceWithRegulatoryCapitalRequirementsUnderBankingRegulationsLineItems" xlink:to="locator_cass_CapitalRequiredForCapitalAdequacyToRiskWeightedAssets1" use="optional" priority="0" order="12"/>
    <loc xlink:type="locator" xlink:href="cass-20201231.xsd#cass_CommonEquityTierOneRiskBasedCapitalRequiredForCapitalAdequacyToRiskWeightedAssets" xlink:label="locator_cass_CommonEquityTierOneRiskBasedCapitalRequiredForCapitalAdequacyToRiskWeightedAssets"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_ComplianceWithRegulatoryCapitalRequirementsUnderBankingRegulationsLineItems" xlink:to="locator_cass_CommonEquityTierOneRiskBasedCapitalRequiredForCapitalAdequacyToRiskWeightedAssets" use="optional" priority="0" order="13"/>
    <loc xlink:type="locator" xlink:href="cass-20201231.xsd#cass_TierOneRiskBasedCapitalRequiredForCapitalAdequacyToRiskWeightedAssets1" xlink:label="locator_cass_TierOneRiskBasedCapitalRequiredForCapitalAdequacyToRiskWeightedAssets1"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_ComplianceWithRegulatoryCapitalRequirementsUnderBankingRegulationsLineItems" xlink:to="locator_cass_TierOneRiskBasedCapitalRequiredForCapitalAdequacyToRiskWeightedAssets1" use="optional" priority="0" order="14"/>
    <loc xlink:type="locator" xlink:href="cass-20201231.xsd#cass_TierOneLeverageCapitalRequiredForCapitalAdequacyToAverageAssets1" xlink:label="locator_cass_TierOneLeverageCapitalRequiredForCapitalAdequacyToAverageAssets1"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_ComplianceWithRegulatoryCapitalRequirementsUnderBankingRegulationsLineItems" xlink:to="locator_cass_TierOneLeverageCapitalRequiredForCapitalAdequacyToAverageAssets1" use="optional" priority="0" order="15"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_CapitalRequiredToBeWellCapitalized" xlink:label="locator_us-gaap_CapitalRequiredToBeWellCapitalized"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_ComplianceWithRegulatoryCapitalRequirementsUnderBankingRegulationsLineItems" xlink:to="locator_us-gaap_CapitalRequiredToBeWellCapitalized" use="optional" priority="0" order="16"/>
    <loc xlink:type="locator" xlink:href="cass-20201231.xsd#cass_CommonEquityTierOneRiskBasedCapitalRequiredToBeWellCapitalized" xlink:label="locator_cass_CommonEquityTierOneRiskBasedCapitalRequiredToBeWellCapitalized"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_ComplianceWithRegulatoryCapitalRequirementsUnderBankingRegulationsLineItems" xlink:to="locator_cass_CommonEquityTierOneRiskBasedCapitalRequiredToBeWellCapitalized" use="optional" priority="0" order="17"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_TierOneRiskBasedCapitalRequiredToBeWellCapitalized" xlink:label="locator_us-gaap_TierOneRiskBasedCapitalRequiredToBeWellCapitalized"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_ComplianceWithRegulatoryCapitalRequirementsUnderBankingRegulationsLineItems" xlink:to="locator_us-gaap_TierOneRiskBasedCapitalRequiredToBeWellCapitalized" use="optional" priority="0" order="18"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_TierOneLeverageCapitalRequiredToBeWellCapitalized" xlink:label="locator_us-gaap_TierOneLeverageCapitalRequiredToBeWellCapitalized"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_ComplianceWithRegulatoryCapitalRequirementsUnderBankingRegulationsLineItems" xlink:to="locator_us-gaap_TierOneLeverageCapitalRequiredToBeWellCapitalized" use="optional" priority="0" order="19"/>
    <loc xlink:type="locator" xlink:href="cass-20201231.xsd#cass_CapitalRequiredToBeWellCapitalizedToRiskWeightedAssets1" xlink:label="locator_cass_CapitalRequiredToBeWellCapitalizedToRiskWeightedAssets1"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_ComplianceWithRegulatoryCapitalRequirementsUnderBankingRegulationsLineItems" xlink:to="locator_cass_CapitalRequiredToBeWellCapitalizedToRiskWeightedAssets1" use="optional" priority="0" order="20"/>
    <loc xlink:type="locator" xlink:href="cass-20201231.xsd#cass_CommonEquityTierOneRiskBasedCapitalRequiredToBeWellCapitalizedToRiskWeightedAssets" xlink:label="locator_cass_CommonEquityTierOneRiskBasedCapitalRequiredToBeWellCapitalizedToRiskWeightedAssets"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_ComplianceWithRegulatoryCapitalRequirementsUnderBankingRegulationsLineItems" xlink:to="locator_cass_CommonEquityTierOneRiskBasedCapitalRequiredToBeWellCapitalizedToRiskWeightedAssets" use="optional" priority="0" order="21"/>
    <loc xlink:type="locator" xlink:href="cass-20201231.xsd#cass_TierOneRiskBasedCapitalRequiredToBeWellCapitalizedToRiskWeightedAssets1" xlink:label="locator_cass_TierOneRiskBasedCapitalRequiredToBeWellCapitalizedToRiskWeightedAssets1"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_ComplianceWithRegulatoryCapitalRequirementsUnderBankingRegulationsLineItems" xlink:to="locator_cass_TierOneRiskBasedCapitalRequiredToBeWellCapitalizedToRiskWeightedAssets1" use="optional" priority="0" order="22"/>
    <loc xlink:type="locator" xlink:href="cass-20201231.xsd#cass_TierOneLeverageCapitalRequiredToBeWellCapitalizedToAverageAssets1" xlink:label="locator_cass_TierOneLeverageCapitalRequiredToBeWellCapitalizedToAverageAssets1"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_ComplianceWithRegulatoryCapitalRequirementsUnderBankingRegulationsLineItems" xlink:to="locator_cass_TierOneLeverageCapitalRequiredToBeWellCapitalizedToAverageAssets1" use="optional" priority="0" order="23"/>
    <loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/dei/2020/dei-2020-01-31.xsd#dei_EntityDomain" xlink:label="locator_dei_EntityDomain_8bfa7d5c-6582-a047-7514-f2f01930b13d_default"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="locator_dei_LegalEntityAxis" xlink:to="locator_dei_EntityDomain_8bfa7d5c-6582-a047-7514-f2f01930b13d_default" use="optional" priority="0" order="30" xbrldt:contextElement="segment"/>
  </definitionLink>
  <definitionLink xlink:type="extended" xlink:role="http://cassinfo.com/role/InvestmentInSecuritiesScheduleOfInvestmentSecuritiesDetails">
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_MarketableSecuritiesLineItems" xlink:label="locator_us-gaap_MarketableSecuritiesLineItems"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_AvailableForSaleSecurities" xlink:label="locator_us-gaap_AvailableForSaleSecurities"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_MarketableSecuritiesLineItems" xlink:to="locator_us-gaap_AvailableForSaleSecurities" use="optional" priority="0" order="0"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_AvailableForSaleSecuritiesAccumulatedGrossUnrealizedGainBeforeTax" xlink:label="locator_us-gaap_AvailableForSaleSecuritiesAccumulatedGrossUnrealizedGainBeforeTax"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_MarketableSecuritiesLineItems" xlink:to="locator_us-gaap_AvailableForSaleSecuritiesAccumulatedGrossUnrealizedGainBeforeTax" use="optional" priority="0" order="1"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_AvailableForSaleSecuritiesAccumulatedGrossUnrealizedLossBeforeTax" xlink:label="locator_us-gaap_AvailableForSaleSecuritiesAccumulatedGrossUnrealizedLossBeforeTax"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_MarketableSecuritiesLineItems" xlink:to="locator_us-gaap_AvailableForSaleSecuritiesAccumulatedGrossUnrealizedLossBeforeTax" use="optional" priority="0" order="2"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_AvailableForSaleSecuritiesAmortizedCost" xlink:label="locator_us-gaap_AvailableForSaleSecuritiesAmortizedCost"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_MarketableSecuritiesLineItems" xlink:to="locator_us-gaap_AvailableForSaleSecuritiesAmortizedCost" use="optional" priority="0" order="3"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_MarketableSecuritiesTable" xlink:label="locator_us-gaap_MarketableSecuritiesTable"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="locator_us-gaap_MarketableSecuritiesLineItems" xlink:to="locator_us-gaap_MarketableSecuritiesTable" use="optional" priority="0" order="10" xbrldt:contextElement="segment" xbrldt:closed="true"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_CashAndCashEquivalentsAxis" xlink:label="locator_us-gaap_CashAndCashEquivalentsAxis"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="locator_us-gaap_MarketableSecuritiesTable" xlink:to="locator_us-gaap_CashAndCashEquivalentsAxis" use="optional" priority="0" order="1"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember" xlink:label="locator_us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="locator_us-gaap_CashAndCashEquivalentsAxis" xlink:to="locator_us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember" use="optional" priority="0" order="20"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_USStatesAndPoliticalSubdivisionsMember" xlink:label="locator_us-gaap_USStatesAndPoliticalSubdivisionsMember"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember" xlink:to="locator_us-gaap_USStatesAndPoliticalSubdivisionsMember" use="optional" priority="0" order="1"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_USGovernmentCorporationsAndAgenciesSecuritiesMember" xlink:label="locator_us-gaap_USGovernmentCorporationsAndAgenciesSecuritiesMember"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember" xlink:to="locator_us-gaap_USGovernmentCorporationsAndAgenciesSecuritiesMember" use="optional" priority="0" order="11"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_CertificatesOfDepositMember" xlink:label="locator_us-gaap_CertificatesOfDepositMember"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember" xlink:to="locator_us-gaap_CertificatesOfDepositMember" use="optional" priority="0" order="51"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember" xlink:label="locator_us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember_2a3e16f8-d8cd-9a6a-aa6a-53d02965050f_default"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="locator_us-gaap_CashAndCashEquivalentsAxis" xlink:to="locator_us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember_2a3e16f8-d8cd-9a6a-aa6a-53d02965050f_default" use="optional" priority="0" order="30" xbrldt:contextElement="segment"/>
  </definitionLink>
  <definitionLink xlink:type="extended" xlink:role="http://cassinfo.com/role/cass-iissofvoswuld1">
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_MarketableSecuritiesLineItems" xlink:label="locator_us-gaap_MarketableSecuritiesLineItems"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionLessThanTwelveMonthsFairValue" xlink:label="locator_us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionLessThanTwelveMonthsFairValue"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_MarketableSecuritiesLineItems" xlink:to="locator_us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionLessThanTwelveMonthsFairValue" use="optional" priority="0" order="0"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionTwelveMonthsOrLongerFairValue" xlink:label="locator_us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionTwelveMonthsOrLongerFairValue"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_MarketableSecuritiesLineItems" xlink:to="locator_us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionTwelveMonthsOrLongerFairValue" use="optional" priority="0" order="1"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionFairValue" xlink:label="locator_us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionFairValue"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_MarketableSecuritiesLineItems" xlink:to="locator_us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionFairValue" use="optional" priority="0" order="2"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionLessThan12MonthsAccumulatedLoss" xlink:label="locator_us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionLessThan12MonthsAccumulatedLoss"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_MarketableSecuritiesLineItems" xlink:to="locator_us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionLessThan12MonthsAccumulatedLoss" use="optional" priority="0" order="3"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPosition12MonthsOrLongerAccumulatedLoss" xlink:label="locator_us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPosition12MonthsOrLongerAccumulatedLoss"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_MarketableSecuritiesLineItems" xlink:to="locator_us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPosition12MonthsOrLongerAccumulatedLoss" use="optional" priority="0" order="4"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionAccumulatedLoss" xlink:label="locator_us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionAccumulatedLoss"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_MarketableSecuritiesLineItems" xlink:to="locator_us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionAccumulatedLoss" use="optional" priority="0" order="5"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_MarketableSecuritiesTable" xlink:label="locator_us-gaap_MarketableSecuritiesTable"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="locator_us-gaap_MarketableSecuritiesLineItems" xlink:to="locator_us-gaap_MarketableSecuritiesTable" use="optional" priority="0" order="10" xbrldt:contextElement="segment" xbrldt:closed="true"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_CashAndCashEquivalentsAxis" xlink:label="locator_us-gaap_CashAndCashEquivalentsAxis"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="locator_us-gaap_MarketableSecuritiesTable" xlink:to="locator_us-gaap_CashAndCashEquivalentsAxis" use="optional" priority="0" order="1"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember" xlink:label="locator_us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="locator_us-gaap_CashAndCashEquivalentsAxis" xlink:to="locator_us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember" use="optional" priority="0" order="20"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_USGovernmentCorporationsAndAgenciesSecuritiesMember" xlink:label="locator_us-gaap_USGovernmentCorporationsAndAgenciesSecuritiesMember"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember" xlink:to="locator_us-gaap_USGovernmentCorporationsAndAgenciesSecuritiesMember" use="optional" priority="0" order="11"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember" xlink:label="locator_us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember_ef140d7c-fae6-d5c6-8a5f-5fb7de5c6fb2_default"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="locator_us-gaap_CashAndCashEquivalentsAxis" xlink:to="locator_us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember_ef140d7c-fae6-d5c6-8a5f-5fb7de5c6fb2_default" use="optional" priority="0" order="30" xbrldt:contextElement="segment"/>
  </definitionLink>
  <definitionLink xlink:type="extended" xlink:role="http://cassinfo.com/role/cass-lsolcd">
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_LoansAndLeasesReceivableDisclosureLineItems" xlink:label="locator_us-gaap_LoansAndLeasesReceivableDisclosureLineItems"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_NotesAndLoansReceivableNetCurrent" xlink:label="locator_us-gaap_NotesAndLoansReceivableNetCurrent"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_LoansAndLeasesReceivableDisclosureLineItems" xlink:to="locator_us-gaap_NotesAndLoansReceivableNetCurrent" use="optional" priority="0" order="0"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_LoansAndLeasesReceivableDisclosureTable" xlink:label="locator_us-gaap_LoansAndLeasesReceivableDisclosureTable"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="locator_us-gaap_LoansAndLeasesReceivableDisclosureLineItems" xlink:to="locator_us-gaap_LoansAndLeasesReceivableDisclosureTable" use="optional" priority="0" order="10" xbrldt:contextElement="segment" xbrldt:closed="true"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FinancialInstrumentAxis" xlink:label="locator_us-gaap_FinancialInstrumentAxis"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="locator_us-gaap_LoansAndLeasesReceivableDisclosureTable" xlink:to="locator_us-gaap_FinancialInstrumentAxis" use="optional" priority="0" order="1"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:label="locator_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="locator_us-gaap_FinancialInstrumentAxis" xlink:to="locator_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" use="optional" priority="0" order="20"/>
    <loc xlink:type="locator" xlink:href="cass-20201231.xsd#cass_CommercialAndIndustrialLoanMember" xlink:label="locator_cass_CommercialAndIndustrialLoanMember"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:to="locator_cass_CommercialAndIndustrialLoanMember" use="optional" priority="0" order="11"/>
    <loc xlink:type="locator" xlink:href="cass-20201231.xsd#cass_RealEstateCommercialMortgageMember" xlink:label="locator_cass_RealEstateCommercialMortgageMember"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:to="locator_cass_RealEstateCommercialMortgageMember" use="optional" priority="0" order="21"/>
    <loc xlink:type="locator" xlink:href="cass-20201231.xsd#cass_RealEstateCommercialConstructionLoanMember" xlink:label="locator_cass_RealEstateCommercialConstructionLoanMember"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:to="locator_cass_RealEstateCommercialConstructionLoanMember" use="optional" priority="0" order="31"/>
    <loc xlink:type="locator" xlink:href="cass-20201231.xsd#cass_RealEstateFaithBasedRelatedMortgageMember" xlink:label="locator_cass_RealEstateFaithBasedRelatedMortgageMember"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:to="locator_cass_RealEstateFaithBasedRelatedMortgageMember" use="optional" priority="0" order="41"/>
    <loc xlink:type="locator" xlink:href="cass-20201231.xsd#cass_RealEstateFaithBasedConstructionLoanMember" xlink:label="locator_cass_RealEstateFaithBasedConstructionLoanMember"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:to="locator_cass_RealEstateFaithBasedConstructionLoanMember" use="optional" priority="0" order="51"/>
    <loc xlink:type="locator" xlink:href="cass-20201231.xsd#cass_PPPMember" xlink:label="locator_cass_PPPMember"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:to="locator_cass_PPPMember" use="optional" priority="0" order="61"/>
    <loc xlink:type="locator" xlink:href="cass-20201231.xsd#cass_OtherLoanMember" xlink:label="locator_cass_OtherLoanMember"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:to="locator_cass_OtherLoanMember" use="optional" priority="0" order="71"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:label="locator_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_4769f97f-5b40-3f24-856d-2e6083f84f7d_default"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="locator_us-gaap_FinancialInstrumentAxis" xlink:to="locator_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_4769f97f-5b40-3f24-856d-2e6083f84f7d_default" use="optional" priority="0" order="30" xbrldt:contextElement="segment"/>
  </definitionLink>
  <definitionLink xlink:type="extended" xlink:role="http://cassinfo.com/role/cass-lsoaolblcd">
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FinancingReceivableRecordedInvestmentPastDueLineItems" xlink:label="locator_us-gaap_FinancingReceivableRecordedInvestmentPastDueLineItems"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FinancingReceivableRecordedInvestmentPastDue" xlink:label="locator_us-gaap_FinancingReceivableRecordedInvestmentPastDue"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_FinancingReceivableRecordedInvestmentPastDueLineItems" xlink:to="locator_us-gaap_FinancingReceivableRecordedInvestmentPastDue" use="optional" priority="0" order="0"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FinancingReceivableRecordedInvestmentNonaccrualStatus" xlink:label="locator_us-gaap_FinancingReceivableRecordedInvestmentNonaccrualStatus"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_FinancingReceivableRecordedInvestmentPastDueLineItems" xlink:to="locator_us-gaap_FinancingReceivableRecordedInvestmentNonaccrualStatus" use="optional" priority="0" order="1"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_NotesAndLoansReceivableNetCurrent" xlink:label="locator_us-gaap_NotesAndLoansReceivableNetCurrent"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_FinancingReceivableRecordedInvestmentPastDueLineItems" xlink:to="locator_us-gaap_NotesAndLoansReceivableNetCurrent" use="optional" priority="0" order="2"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ScheduleOfFinancingReceivablesPastDueTable" xlink:label="locator_us-gaap_ScheduleOfFinancingReceivablesPastDueTable"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="locator_us-gaap_FinancingReceivableRecordedInvestmentPastDueLineItems" xlink:to="locator_us-gaap_ScheduleOfFinancingReceivablesPastDueTable" use="optional" priority="0" order="10" xbrldt:contextElement="segment" xbrldt:closed="true"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FinancingReceivablesPeriodPastDueAxis" xlink:label="locator_us-gaap_FinancingReceivablesPeriodPastDueAxis"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="locator_us-gaap_ScheduleOfFinancingReceivablesPastDueTable" xlink:to="locator_us-gaap_FinancingReceivablesPeriodPastDueAxis" use="optional" priority="0" order="1"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FinancingReceivablesPeriodPastDueDomain" xlink:label="locator_us-gaap_FinancingReceivablesPeriodPastDueDomain"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="locator_us-gaap_FinancingReceivablesPeriodPastDueAxis" xlink:to="locator_us-gaap_FinancingReceivablesPeriodPastDueDomain" use="optional" priority="0" order="20"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FinancingReceivables1To29DaysPastDueMember" xlink:label="locator_us-gaap_FinancingReceivables1To29DaysPastDueMember"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_FinancingReceivablesPeriodPastDueDomain" xlink:to="locator_us-gaap_FinancingReceivables1To29DaysPastDueMember" use="optional" priority="0" order="81"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FinancingReceivables30To59DaysPastDueMember" xlink:label="locator_us-gaap_FinancingReceivables30To59DaysPastDueMember"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_FinancingReceivablesPeriodPastDueDomain" xlink:to="locator_us-gaap_FinancingReceivables30To59DaysPastDueMember" use="optional" priority="0" order="161"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FinancingReceivables60To89DaysPastDueMember" xlink:label="locator_us-gaap_FinancingReceivables60To89DaysPastDueMember"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_FinancingReceivablesPeriodPastDueDomain" xlink:to="locator_us-gaap_FinancingReceivables60To89DaysPastDueMember" use="optional" priority="0" order="241"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FinancingReceivablesEqualToGreaterThan90DaysPastDueMember" xlink:label="locator_us-gaap_FinancingReceivablesEqualToGreaterThan90DaysPastDueMember"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_FinancingReceivablesPeriodPastDueDomain" xlink:to="locator_us-gaap_FinancingReceivablesEqualToGreaterThan90DaysPastDueMember" use="optional" priority="0" order="321"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis" xlink:label="locator_us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="locator_us-gaap_ScheduleOfFinancingReceivablesPastDueTable" xlink:to="locator_us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis" use="optional" priority="0" order="2"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" xlink:label="locator_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="locator_us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis" xlink:to="locator_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" use="optional" priority="0" order="20"/>
    <loc xlink:type="locator" xlink:href="cass-20201231.xsd#cass_CommercialAndIndustrialLoanMember" xlink:label="locator_cass_CommercialAndIndustrialLoanMember"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" xlink:to="locator_cass_CommercialAndIndustrialLoanMember" use="optional" priority="0" order="11"/>
    <loc xlink:type="locator" xlink:href="cass-20201231.xsd#cass_RealEstateCommercialMortgageMember" xlink:label="locator_cass_RealEstateCommercialMortgageMember"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" xlink:to="locator_cass_RealEstateCommercialMortgageMember" use="optional" priority="0" order="21"/>
    <loc xlink:type="locator" xlink:href="cass-20201231.xsd#cass_RealEstateCommercialConstructionLoanMember" xlink:label="locator_cass_RealEstateCommercialConstructionLoanMember"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" xlink:to="locator_cass_RealEstateCommercialConstructionLoanMember" use="optional" priority="0" order="31"/>
    <loc xlink:type="locator" xlink:href="cass-20201231.xsd#cass_RealEstateFaithBasedRelatedMortgageMember" xlink:label="locator_cass_RealEstateFaithBasedRelatedMortgageMember"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" xlink:to="locator_cass_RealEstateFaithBasedRelatedMortgageMember" use="optional" priority="0" order="41"/>
    <loc xlink:type="locator" xlink:href="cass-20201231.xsd#cass_RealEstateFaithBasedConstructionLoanMember" xlink:label="locator_cass_RealEstateFaithBasedConstructionLoanMember"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" xlink:to="locator_cass_RealEstateFaithBasedConstructionLoanMember" use="optional" priority="0" order="51"/>
    <loc xlink:type="locator" xlink:href="cass-20201231.xsd#cass_IndustrialRevenueBondsMember" xlink:label="locator_cass_IndustrialRevenueBondsMember"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" xlink:to="locator_cass_IndustrialRevenueBondsMember" use="optional" priority="0" order="61"/>
    <loc xlink:type="locator" xlink:href="cass-20201231.xsd#cass_OtherFinancingReceivableMember" xlink:label="locator_cass_OtherFinancingReceivableMember"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" xlink:to="locator_cass_OtherFinancingReceivableMember" use="optional" priority="0" order="71"/>
    <loc xlink:type="locator" xlink:href="cass-20201231.xsd#cass_PPPMember" xlink:label="locator_cass_PPPMember"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" xlink:to="locator_cass_PPPMember" use="optional" priority="0" order="461"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FinancingReceivablesPeriodPastDueDomain" xlink:label="locator_us-gaap_FinancingReceivablesPeriodPastDueDomain_7a1314d3-8e91-69ad-1d2c-9544397daf96_default"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="locator_us-gaap_FinancingReceivablesPeriodPastDueAxis" xlink:to="locator_us-gaap_FinancingReceivablesPeriodPastDueDomain_7a1314d3-8e91-69ad-1d2c-9544397daf96_default" use="optional" priority="0" order="30" xbrldt:contextElement="segment"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" xlink:label="locator_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_ad41fa5a-4f30-dde2-906a-80713c053476_default"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="locator_us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis" xlink:to="locator_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_ad41fa5a-4f30-dde2-906a-80713c053476_default" use="optional" priority="0" order="30" xbrldt:contextElement="segment"/>
  </definitionLink>
  <definitionLink xlink:type="extended" xlink:role="http://cassinfo.com/role/cass-lsoceolpd">
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FinancingReceivableRecordedInvestmentLineItems" xlink:label="locator_us-gaap_FinancingReceivableRecordedInvestmentLineItems"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_NotesAndLoansReceivableNetCurrent" xlink:label="locator_us-gaap_NotesAndLoansReceivableNetCurrent"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_FinancingReceivableRecordedInvestmentLineItems" xlink:to="locator_us-gaap_NotesAndLoansReceivableNetCurrent" use="optional" priority="0" order="0"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ScheduleOfFinancingReceivableRecordedInvestmentCreditQualityIndicatorTable" xlink:label="locator_us-gaap_ScheduleOfFinancingReceivableRecordedInvestmentCreditQualityIndicatorTable"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="locator_us-gaap_FinancingReceivableRecordedInvestmentLineItems" xlink:to="locator_us-gaap_ScheduleOfFinancingReceivableRecordedInvestmentCreditQualityIndicatorTable" use="optional" priority="0" order="10" xbrldt:contextElement="segment" xbrldt:closed="true"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis" xlink:label="locator_us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="locator_us-gaap_ScheduleOfFinancingReceivableRecordedInvestmentCreditQualityIndicatorTable" xlink:to="locator_us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis" use="optional" priority="0" order="1"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" xlink:label="locator_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="locator_us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis" xlink:to="locator_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" use="optional" priority="0" order="20"/>
    <loc xlink:type="locator" xlink:href="cass-20201231.xsd#cass_CommercialAndIndustrialLoanMember" xlink:label="locator_cass_CommercialAndIndustrialLoanMember"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" xlink:to="locator_cass_CommercialAndIndustrialLoanMember" use="optional" priority="0" order="41"/>
    <loc xlink:type="locator" xlink:href="cass-20201231.xsd#cass_RealEstateCommercialMortgageMember" xlink:label="locator_cass_RealEstateCommercialMortgageMember"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" xlink:to="locator_cass_RealEstateCommercialMortgageMember" use="optional" priority="0" order="81"/>
    <loc xlink:type="locator" xlink:href="cass-20201231.xsd#cass_RealEstateCommercialConstructionLoanMember" xlink:label="locator_cass_RealEstateCommercialConstructionLoanMember"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" xlink:to="locator_cass_RealEstateCommercialConstructionLoanMember" use="optional" priority="0" order="121"/>
    <loc xlink:type="locator" xlink:href="cass-20201231.xsd#cass_RealEstateChurchRelatedConstructionLoanMember" xlink:label="locator_cass_RealEstateChurchRelatedConstructionLoanMember"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" xlink:to="locator_cass_RealEstateChurchRelatedConstructionLoanMember" use="optional" priority="0" order="142"/>
    <loc xlink:type="locator" xlink:href="cass-20201231.xsd#cass_RealEstateFaithBasedRelatedMortgageMember" xlink:label="locator_cass_RealEstateFaithBasedRelatedMortgageMember"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" xlink:to="locator_cass_RealEstateFaithBasedRelatedMortgageMember" use="optional" priority="0" order="161"/>
    <loc xlink:type="locator" xlink:href="cass-20201231.xsd#cass_RealEstateFaithBasedConstructionLoanMember" xlink:label="locator_cass_RealEstateFaithBasedConstructionLoanMember"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" xlink:to="locator_cass_RealEstateFaithBasedConstructionLoanMember" use="optional" priority="0" order="201"/>
    <loc xlink:type="locator" xlink:href="cass-20201231.xsd#cass_IndustrialRevenueBondsMember" xlink:label="locator_cass_IndustrialRevenueBondsMember"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" xlink:to="locator_cass_IndustrialRevenueBondsMember" use="optional" priority="0" order="241"/>
    <loc xlink:type="locator" xlink:href="cass-20201231.xsd#cass_OtherFinancingReceivableMember" xlink:label="locator_cass_OtherFinancingReceivableMember"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" xlink:to="locator_cass_OtherFinancingReceivableMember" use="optional" priority="0" order="281"/>
    <loc xlink:type="locator" xlink:href="cass-20201231.xsd#cass_PPPMember" xlink:label="locator_cass_PPPMember"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" xlink:to="locator_cass_PPPMember" use="optional" priority="0" order="561"/>
    <loc xlink:type="locator" xlink:href="cass-20201231.xsd#cass_CreditExposureOfLoanPortfolioAxis" xlink:label="locator_cass_CreditExposureOfLoanPortfolioAxis"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="locator_us-gaap_ScheduleOfFinancingReceivableRecordedInvestmentCreditQualityIndicatorTable" xlink:to="locator_cass_CreditExposureOfLoanPortfolioAxis" use="optional" priority="0" order="2"/>
    <loc xlink:type="locator" xlink:href="cass-20201231.xsd#cass_CreditExposureOfLoanPortfolioDomain" xlink:label="locator_cass_CreditExposureOfLoanPortfolioDomain"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="locator_cass_CreditExposureOfLoanPortfolioAxis" xlink:to="locator_cass_CreditExposureOfLoanPortfolioDomain" use="optional" priority="0" order="20"/>
    <loc xlink:type="locator" xlink:href="cass-20201231.xsd#cass_LoansSubjectToNormalMonitoringMember" xlink:label="locator_cass_LoansSubjectToNormalMonitoringMember"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_cass_CreditExposureOfLoanPortfolioDomain" xlink:to="locator_cass_LoansSubjectToNormalMonitoringMember" use="optional" priority="0" order="11"/>
    <loc xlink:type="locator" xlink:href="cass-20201231.xsd#cass_PerformingLoansSubjectToSpecialMonitoringMember" xlink:label="locator_cass_PerformingLoansSubjectToSpecialMonitoringMember"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_cass_CreditExposureOfLoanPortfolioDomain" xlink:to="locator_cass_PerformingLoansSubjectToSpecialMonitoringMember" use="optional" priority="0" order="21"/>
    <loc xlink:type="locator" xlink:href="cass-20201231.xsd#cass_NonperformingLoansSubjectToSpecialMonitoringMember" xlink:label="locator_cass_NonperformingLoansSubjectToSpecialMonitoringMember"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_cass_CreditExposureOfLoanPortfolioDomain" xlink:to="locator_cass_NonperformingLoansSubjectToSpecialMonitoringMember" use="optional" priority="0" order="31"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" xlink:label="locator_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_ce375738-8c14-b8ed-e825-47189d5088ad_default"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="locator_us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis" xlink:to="locator_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_ce375738-8c14-b8ed-e825-47189d5088ad_default" use="optional" priority="0" order="30" xbrldt:contextElement="segment"/>
    <loc xlink:type="locator" xlink:href="cass-20201231.xsd#cass_CreditExposureOfLoanPortfolioDomain" xlink:label="locator_cass_CreditExposureOfLoanPortfolioDomain_ea1c90d6-9b6c-cfb0-3b7d-33516b3ad8a5_default"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="locator_cass_CreditExposureOfLoanPortfolioAxis" xlink:to="locator_cass_CreditExposureOfLoanPortfolioDomain_ea1c90d6-9b6c-cfb0-3b7d-33516b3ad8a5_default" use="optional" priority="0" order="30" xbrldt:contextElement="segment"/>
  </definitionLink>
  <definitionLink xlink:type="extended" xlink:role="http://cassinfo.com/role/LoansSummaryOfCategoryOfLoansConsideredAsTroubledDebtRestructuringDetails">
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FinancingReceivableAllowanceForCreditLossesLineItems" xlink:label="locator_us-gaap_FinancingReceivableAllowanceForCreditLossesLineItems"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FinancingReceivableModificationsNumberOfContracts2" xlink:label="locator_us-gaap_FinancingReceivableModificationsNumberOfContracts2"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_FinancingReceivableAllowanceForCreditLossesLineItems" xlink:to="locator_us-gaap_FinancingReceivableModificationsNumberOfContracts2" use="optional" priority="0" order="0"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FinancingReceivableModificationsPreModificationRecordedInvestment2" xlink:label="locator_us-gaap_FinancingReceivableModificationsPreModificationRecordedInvestment2"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_FinancingReceivableAllowanceForCreditLossesLineItems" xlink:to="locator_us-gaap_FinancingReceivableModificationsPreModificationRecordedInvestment2" use="optional" priority="0" order="1"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FinancingReceivableModificationsPostModificationRecordedInvestment2" xlink:label="locator_us-gaap_FinancingReceivableModificationsPostModificationRecordedInvestment2"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_FinancingReceivableAllowanceForCreditLossesLineItems" xlink:to="locator_us-gaap_FinancingReceivableModificationsPostModificationRecordedInvestment2" use="optional" priority="0" order="2"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ScheduleOfFinancingReceivableAllowanceForCreditLossesTable" xlink:label="locator_us-gaap_ScheduleOfFinancingReceivableAllowanceForCreditLossesTable"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="locator_us-gaap_FinancingReceivableAllowanceForCreditLossesLineItems" xlink:to="locator_us-gaap_ScheduleOfFinancingReceivableAllowanceForCreditLossesTable" use="optional" priority="0" order="10" xbrldt:contextElement="segment" xbrldt:closed="true"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis" xlink:label="locator_us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="locator_us-gaap_ScheduleOfFinancingReceivableAllowanceForCreditLossesTable" xlink:to="locator_us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis" use="optional" priority="0" order="1"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" xlink:label="locator_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="locator_us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis" xlink:to="locator_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" use="optional" priority="0" order="20"/>
    <loc xlink:type="locator" xlink:href="cass-20201231.xsd#cass_CommercialAndIndustrialLoanMember" xlink:label="locator_cass_CommercialAndIndustrialLoanMember"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" xlink:to="locator_cass_CommercialAndIndustrialLoanMember" use="optional" priority="0" order="11"/>
    <loc xlink:type="locator" xlink:href="cass-20201231.xsd#cass_FaithBasedRealEstateMember" xlink:label="locator_cass_FaithBasedRealEstateMember"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" xlink:to="locator_cass_FaithBasedRealEstateMember" use="optional" priority="0" order="21"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" xlink:label="locator_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_e1368860-1f62-5188-939f-fd5bd617034d_default"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="locator_us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis" xlink:to="locator_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_e1368860-1f62-5188-939f-fd5bd617034d_default" use="optional" priority="0" order="30" xbrldt:contextElement="segment"/>
  </definitionLink>
  <definitionLink xlink:type="extended" xlink:role="http://cassinfo.com/role/LoansSummaryOfAclByCategoryDetails">
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FinancingReceivableAllowanceForCreditLossesLineItems" xlink:label="locator_us-gaap_FinancingReceivableAllowanceForCreditLossesLineItems"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FinancingReceivableAllowanceForCreditLosses" xlink:label="locator_us-gaap_FinancingReceivableAllowanceForCreditLosses"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_FinancingReceivableAllowanceForCreditLossesLineItems" xlink:to="locator_us-gaap_FinancingReceivableAllowanceForCreditLosses" use="optional" priority="0" order="0"/>
    <loc xlink:type="locator" xlink:href="cass-20201231.xsd#cass_FinancingReceivableAllowanceForCreditLossesCumulativeEffectOfAccountingChange" xlink:label="locator_cass_FinancingReceivableAllowanceForCreditLossesCumulativeEffectOfAccountingChange"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_FinancingReceivableAllowanceForCreditLossesLineItems" xlink:to="locator_cass_FinancingReceivableAllowanceForCreditLossesCumulativeEffectOfAccountingChange" use="optional" priority="0" order="1"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ProvisionForLoanLeaseAndOtherLosses" xlink:label="locator_us-gaap_ProvisionForLoanLeaseAndOtherLosses"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_FinancingReceivableAllowanceForCreditLossesLineItems" xlink:to="locator_us-gaap_ProvisionForLoanLeaseAndOtherLosses" use="optional" priority="0" order="2"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FinancingReceivableAllowanceForCreditLossesRecovery" xlink:label="locator_us-gaap_FinancingReceivableAllowanceForCreditLossesRecovery"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_FinancingReceivableAllowanceForCreditLossesLineItems" xlink:to="locator_us-gaap_FinancingReceivableAllowanceForCreditLossesRecovery" use="optional" priority="0" order="3"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ScheduleOfFinancingReceivableAllowanceForCreditLossesTable" xlink:label="locator_us-gaap_ScheduleOfFinancingReceivableAllowanceForCreditLossesTable"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="locator_us-gaap_FinancingReceivableAllowanceForCreditLossesLineItems" xlink:to="locator_us-gaap_ScheduleOfFinancingReceivableAllowanceForCreditLossesTable" use="optional" priority="0" order="10" xbrldt:contextElement="segment" xbrldt:closed="true"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis" xlink:label="locator_us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="locator_us-gaap_ScheduleOfFinancingReceivableAllowanceForCreditLossesTable" xlink:to="locator_us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis" use="optional" priority="0" order="1"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" xlink:label="locator_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="locator_us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis" xlink:to="locator_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" use="optional" priority="0" order="20"/>
    <loc xlink:type="locator" xlink:href="cass-20201231.xsd#cass_CAndIMember" xlink:label="locator_cass_CAndIMember"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" xlink:to="locator_cass_CAndIMember" use="optional" priority="0" order="1"/>
    <loc xlink:type="locator" xlink:href="cass-20201231.xsd#cass_CREMember" xlink:label="locator_cass_CREMember"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" xlink:to="locator_cass_CREMember" use="optional" priority="0" order="11"/>
    <loc xlink:type="locator" xlink:href="cass-20201231.xsd#cass_FaithBasedCREMember" xlink:label="locator_cass_FaithBasedCREMember"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" xlink:to="locator_cass_FaithBasedCREMember" use="optional" priority="0" order="21"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ConstructionMember" xlink:label="locator_us-gaap_ConstructionMember"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" xlink:to="locator_us-gaap_ConstructionMember" use="optional" priority="0" order="31"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" xlink:label="locator_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_9b9e08b1-a310-c49d-1480-95f63c4820f2_default"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="locator_us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis" xlink:to="locator_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_9b9e08b1-a310-c49d-1480-95f63c4820f2_default" use="optional" priority="0" order="30" xbrldt:contextElement="segment"/>
  </definitionLink>
  <definitionLink xlink:type="extended" xlink:role="http://cassinfo.com/role/LoansSummaryOfAllowanceForLoanLossesDetails">
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FinancingReceivableAllowanceForCreditLossesLineItems" xlink:label="locator_us-gaap_FinancingReceivableAllowanceForCreditLossesLineItems"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_LoansAndLeasesReceivableAllowance" xlink:label="locator_us-gaap_LoansAndLeasesReceivableAllowance"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_FinancingReceivableAllowanceForCreditLossesLineItems" xlink:to="locator_us-gaap_LoansAndLeasesReceivableAllowance" use="optional" priority="0" order="0"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_AllowanceForLoanAndLeaseLossesWriteOffs" xlink:label="locator_us-gaap_AllowanceForLoanAndLeaseLossesWriteOffs"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_FinancingReceivableAllowanceForCreditLossesLineItems" xlink:to="locator_us-gaap_AllowanceForLoanAndLeaseLossesWriteOffs" use="optional" priority="0" order="1"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_AllowanceForLoanAndLeaseLossRecoveryOfBadDebts" xlink:label="locator_us-gaap_AllowanceForLoanAndLeaseLossRecoveryOfBadDebts"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_FinancingReceivableAllowanceForCreditLossesLineItems" xlink:to="locator_us-gaap_AllowanceForLoanAndLeaseLossRecoveryOfBadDebts" use="optional" priority="0" order="2"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ProvisionForLoanAndLeaseLosses" xlink:label="locator_us-gaap_ProvisionForLoanAndLeaseLosses"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_FinancingReceivableAllowanceForCreditLossesLineItems" xlink:to="locator_us-gaap_ProvisionForLoanAndLeaseLosses" use="optional" priority="0" order="3"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ScheduleOfFinancingReceivableAllowanceForCreditLossesTable" xlink:label="locator_us-gaap_ScheduleOfFinancingReceivableAllowanceForCreditLossesTable"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="locator_us-gaap_FinancingReceivableAllowanceForCreditLossesLineItems" xlink:to="locator_us-gaap_ScheduleOfFinancingReceivableAllowanceForCreditLossesTable" use="optional" priority="0" order="10" xbrldt:contextElement="segment" xbrldt:closed="true"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis" xlink:label="locator_us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="locator_us-gaap_ScheduleOfFinancingReceivableAllowanceForCreditLossesTable" xlink:to="locator_us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis" use="optional" priority="0" order="1"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" xlink:label="locator_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="locator_us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis" xlink:to="locator_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" use="optional" priority="0" order="20"/>
    <loc xlink:type="locator" xlink:href="cass-20201231.xsd#cass_CommercialAndIndustrialLoanMember" xlink:label="locator_cass_CommercialAndIndustrialLoanMember"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" xlink:to="locator_cass_CommercialAndIndustrialLoanMember" use="optional" priority="0" order="1"/>
    <loc xlink:type="locator" xlink:href="cass-20201231.xsd#cass_RealEstateCommercialMortgageMember" xlink:label="locator_cass_RealEstateCommercialMortgageMember"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" xlink:to="locator_cass_RealEstateCommercialMortgageMember" use="optional" priority="0" order="11"/>
    <loc xlink:type="locator" xlink:href="cass-20201231.xsd#cass_RealEstateCommercialConstructionLoanMember" xlink:label="locator_cass_RealEstateCommercialConstructionLoanMember"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" xlink:to="locator_cass_RealEstateCommercialConstructionLoanMember" use="optional" priority="0" order="21"/>
    <loc xlink:type="locator" xlink:href="cass-20201231.xsd#cass_RealEstateFaithBasedRelatedMortgageMember" xlink:label="locator_cass_RealEstateFaithBasedRelatedMortgageMember"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" xlink:to="locator_cass_RealEstateFaithBasedRelatedMortgageMember" use="optional" priority="0" order="31"/>
    <loc xlink:type="locator" xlink:href="cass-20201231.xsd#cass_RealEstateFaithBasedConstructionLoanMember" xlink:label="locator_cass_RealEstateFaithBasedConstructionLoanMember"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" xlink:to="locator_cass_RealEstateFaithBasedConstructionLoanMember" use="optional" priority="0" order="41"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain" xlink:label="locator_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_546eca51-8c93-30b2-1a66-9ac074b3f5e9_default"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="locator_us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis" xlink:to="locator_us-gaap_FinancingReceivableRecordedInvestmentClassOfFinancingReceivableDomain_546eca51-8c93-30b2-1a66-9ac074b3f5e9_default" use="optional" priority="0" order="30" xbrldt:contextElement="segment"/>
  </definitionLink>
  <definitionLink xlink:type="extended" xlink:role="http://cassinfo.com/role/cass-paesopaed">
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_PropertyPlantAndEquipmentLineItems" xlink:label="locator_us-gaap_PropertyPlantAndEquipmentLineItems"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_PropertyPlantAndEquipmentGross" xlink:label="locator_us-gaap_PropertyPlantAndEquipmentGross"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_PropertyPlantAndEquipmentLineItems" xlink:to="locator_us-gaap_PropertyPlantAndEquipmentGross" use="optional" priority="0" order="0"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment" xlink:label="locator_us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_PropertyPlantAndEquipmentLineItems" xlink:to="locator_us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment" use="optional" priority="0" order="1"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_PropertyPlantAndEquipmentNet" xlink:label="locator_us-gaap_PropertyPlantAndEquipmentNet"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_PropertyPlantAndEquipmentLineItems" xlink:to="locator_us-gaap_PropertyPlantAndEquipmentNet" use="optional" priority="0" order="2"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ScheduleOfPropertyPlantAndEquipmentTable" xlink:label="locator_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="locator_us-gaap_PropertyPlantAndEquipmentLineItems" xlink:to="locator_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable" use="optional" priority="0" order="10" xbrldt:contextElement="segment" xbrldt:closed="true"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_PropertyPlantAndEquipmentByTypeAxis" xlink:label="locator_us-gaap_PropertyPlantAndEquipmentByTypeAxis"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="locator_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable" xlink:to="locator_us-gaap_PropertyPlantAndEquipmentByTypeAxis" use="optional" priority="0" order="1"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_PropertyPlantAndEquipmentTypeDomain" xlink:label="locator_us-gaap_PropertyPlantAndEquipmentTypeDomain"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="locator_us-gaap_PropertyPlantAndEquipmentByTypeAxis" xlink:to="locator_us-gaap_PropertyPlantAndEquipmentTypeDomain" use="optional" priority="0" order="20"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_LandMember" xlink:label="locator_us-gaap_LandMember"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_PropertyPlantAndEquipmentTypeDomain" xlink:to="locator_us-gaap_LandMember" use="optional" priority="0" order="11"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_BuildingMember" xlink:label="locator_us-gaap_BuildingMember"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_PropertyPlantAndEquipmentTypeDomain" xlink:to="locator_us-gaap_BuildingMember" use="optional" priority="0" order="21"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_LeaseholdsAndLeaseholdImprovementsMember" xlink:label="locator_us-gaap_LeaseholdsAndLeaseholdImprovementsMember"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_PropertyPlantAndEquipmentTypeDomain" xlink:to="locator_us-gaap_LeaseholdsAndLeaseholdImprovementsMember" use="optional" priority="0" order="31"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FurnitureAndFixturesMember" xlink:label="locator_us-gaap_FurnitureAndFixturesMember"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_PropertyPlantAndEquipmentTypeDomain" xlink:to="locator_us-gaap_FurnitureAndFixturesMember" use="optional" priority="0" order="41"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ComputerSoftwareIntangibleAssetMember" xlink:label="locator_us-gaap_ComputerSoftwareIntangibleAssetMember"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_PropertyPlantAndEquipmentTypeDomain" xlink:to="locator_us-gaap_ComputerSoftwareIntangibleAssetMember" use="optional" priority="0" order="51"/>
    <loc xlink:type="locator" xlink:href="cass-20201231.xsd#cass_InternallyDevelopedSoftwareMember" xlink:label="locator_cass_InternallyDevelopedSoftwareMember"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_PropertyPlantAndEquipmentTypeDomain" xlink:to="locator_cass_InternallyDevelopedSoftwareMember" use="optional" priority="0" order="61"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_PropertyPlantAndEquipmentTypeDomain" xlink:label="locator_us-gaap_PropertyPlantAndEquipmentTypeDomain_c8f5b0bb-2ac9-83bb-e24a-a99e6212b5f8_default"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="locator_us-gaap_PropertyPlantAndEquipmentByTypeAxis" xlink:to="locator_us-gaap_PropertyPlantAndEquipmentTypeDomain_c8f5b0bb-2ac9-83bb-e24a-a99e6212b5f8_default" use="optional" priority="0" order="30" xbrldt:contextElement="segment"/>
  </definitionLink>
  <definitionLink xlink:type="extended" xlink:role="http://cassinfo.com/role/AcquiredIntangibleAssetsNarrativeDetails">
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_AcquiredFiniteLivedIntangibleAssetsLineItems" xlink:label="locator_us-gaap_AcquiredFiniteLivedIntangibleAssetsLineItems"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FinitelivedIntangibleAssetsAcquired1" xlink:label="locator_us-gaap_FinitelivedIntangibleAssetsAcquired1"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_AcquiredFiniteLivedIntangibleAssetsLineItems" xlink:to="locator_us-gaap_FinitelivedIntangibleAssetsAcquired1" use="optional" priority="0" order="0"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetUsefulLife" xlink:label="locator_us-gaap_FiniteLivedIntangibleAssetUsefulLife"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_AcquiredFiniteLivedIntangibleAssetsLineItems" xlink:to="locator_us-gaap_FiniteLivedIntangibleAssetUsefulLife" use="optional" priority="0" order="1"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_AmortizationOfIntangibleAssets" xlink:label="locator_us-gaap_AmortizationOfIntangibleAssets"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_AcquiredFiniteLivedIntangibleAssetsLineItems" xlink:to="locator_us-gaap_AmortizationOfIntangibleAssets" use="optional" priority="0" order="2"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseNextTwelveMonths" xlink:label="locator_us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseNextTwelveMonths"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_AcquiredFiniteLivedIntangibleAssetsLineItems" xlink:to="locator_us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseNextTwelveMonths" use="optional" priority="0" order="3"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearTwo" xlink:label="locator_us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearTwo"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_AcquiredFiniteLivedIntangibleAssetsLineItems" xlink:to="locator_us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearTwo" use="optional" priority="0" order="4"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearThree" xlink:label="locator_us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearThree"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_AcquiredFiniteLivedIntangibleAssetsLineItems" xlink:to="locator_us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearThree" use="optional" priority="0" order="5"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearFour" xlink:label="locator_us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearFour"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_AcquiredFiniteLivedIntangibleAssetsLineItems" xlink:to="locator_us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearFour" use="optional" priority="0" order="6"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseAfterYearFive" xlink:label="locator_us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseAfterYearFive"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_AcquiredFiniteLivedIntangibleAssetsLineItems" xlink:to="locator_us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseAfterYearFive" use="optional" priority="0" order="7"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIntangibleAssetsOtherThanGoodwill" xlink:label="locator_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIntangibleAssetsOtherThanGoodwill"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_AcquiredFiniteLivedIntangibleAssetsLineItems" xlink:to="locator_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIntangibleAssetsOtherThanGoodwill" use="optional" priority="0" order="8"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_PaymentsToAcquireBusinessesGross" xlink:label="locator_us-gaap_PaymentsToAcquireBusinessesGross"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_AcquiredFiniteLivedIntangibleAssetsLineItems" xlink:to="locator_us-gaap_PaymentsToAcquireBusinessesGross" use="optional" priority="0" order="9"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ScheduleOfAcquiredFiniteLivedIntangibleAssetByMajorClassTable" xlink:label="locator_us-gaap_ScheduleOfAcquiredFiniteLivedIntangibleAssetByMajorClassTable"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="locator_us-gaap_AcquiredFiniteLivedIntangibleAssetsLineItems" xlink:to="locator_us-gaap_ScheduleOfAcquiredFiniteLivedIntangibleAssetByMajorClassTable" use="optional" priority="0" order="10" xbrldt:contextElement="segment" xbrldt:closed="true"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis" xlink:label="locator_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="locator_us-gaap_ScheduleOfAcquiredFiniteLivedIntangibleAssetByMajorClassTable" xlink:to="locator_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis" use="optional" priority="0" order="1"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain" xlink:label="locator_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="locator_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis" xlink:to="locator_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain" use="optional" priority="0" order="20"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_CustomerListsMember" xlink:label="locator_us-gaap_CustomerListsMember"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain" xlink:to="locator_us-gaap_CustomerListsMember" use="optional" priority="0" order="1"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_PatentsMember" xlink:label="locator_us-gaap_PatentsMember"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain" xlink:to="locator_us-gaap_PatentsMember" use="optional" priority="0" order="21"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_NoncompeteAgreementsMember" xlink:label="locator_us-gaap_NoncompeteAgreementsMember"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain" xlink:to="locator_us-gaap_NoncompeteAgreementsMember" use="optional" priority="0" order="31"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ComputerSoftwareIntangibleAssetMember" xlink:label="locator_us-gaap_ComputerSoftwareIntangibleAssetMember"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain" xlink:to="locator_us-gaap_ComputerSoftwareIntangibleAssetMember" use="optional" priority="0" order="51"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_TradeNamesMember" xlink:label="locator_us-gaap_TradeNamesMember"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain" xlink:to="locator_us-gaap_TradeNamesMember" use="optional" priority="0" order="81"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_OtherIntangibleAssetsMember" xlink:label="locator_us-gaap_OtherIntangibleAssetsMember"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain" xlink:to="locator_us-gaap_OtherIntangibleAssetsMember" use="optional" priority="0" order="91"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_GoodwillMember" xlink:label="locator_us-gaap_GoodwillMember"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain" xlink:to="locator_us-gaap_GoodwillMember" use="optional" priority="0" order="171"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/srt/2020/elts/srt-2020-01-31.xsd#srt_RangeAxis" xlink:label="locator_srt_RangeAxis"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="locator_us-gaap_ScheduleOfAcquiredFiniteLivedIntangibleAssetByMajorClassTable" xlink:to="locator_srt_RangeAxis" use="optional" priority="0" order="2"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/srt/2020/elts/srt-2020-01-31.xsd#srt_RangeMember" xlink:label="locator_srt_RangeMember"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="locator_srt_RangeAxis" xlink:to="locator_srt_RangeMember" use="optional" priority="0" order="20"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/srt/2020/elts/srt-2020-01-31.xsd#srt_MinimumMember" xlink:label="locator_srt_MinimumMember"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_srt_RangeMember" xlink:to="locator_srt_MinimumMember" use="optional" priority="0" order="2"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/srt/2020/elts/srt-2020-01-31.xsd#srt_MaximumMember" xlink:label="locator_srt_MaximumMember"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_srt_RangeMember" xlink:to="locator_srt_MaximumMember" use="optional" priority="0" order="12"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_BusinessAcquisitionAxis" xlink:label="locator_us-gaap_BusinessAcquisitionAxis"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="locator_us-gaap_ScheduleOfAcquiredFiniteLivedIntangibleAssetByMajorClassTable" xlink:to="locator_us-gaap_BusinessAcquisitionAxis" use="optional" priority="0" order="3"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_BusinessAcquisitionAcquireeDomain" xlink:label="locator_us-gaap_BusinessAcquisitionAcquireeDomain"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="locator_us-gaap_BusinessAcquisitionAxis" xlink:to="locator_us-gaap_BusinessAcquisitionAcquireeDomain" use="optional" priority="0" order="20"/>
    <loc xlink:type="locator" xlink:href="cass-20201231.xsd#cass_GatewayGivingLLCMember" xlink:label="locator_cass_GatewayGivingLLCMember"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_BusinessAcquisitionAcquireeDomain" xlink:to="locator_cass_GatewayGivingLLCMember" use="optional" priority="0" order="141"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_BusinessCombinationConsiderationTransferred1" xlink:label="locator_us-gaap_BusinessCombinationConsiderationTransferred1"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_AcquiredFiniteLivedIntangibleAssetsLineItems" xlink:to="locator_us-gaap_BusinessCombinationConsiderationTransferred1" use="optional" priority="0" order="10"/>
    <loc xlink:type="locator" xlink:href="cass-20201231.xsd#cass_EstimatedEarnoutAmount" xlink:label="locator_cass_EstimatedEarnoutAmount"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_AcquiredFiniteLivedIntangibleAssetsLineItems" xlink:to="locator_cass_EstimatedEarnoutAmount" use="optional" priority="0" order="11"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain" xlink:label="locator_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_40c952b1-d573-4958-d586-1f9966f00b9d_default"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="locator_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis" xlink:to="locator_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_40c952b1-d573-4958-d586-1f9966f00b9d_default" use="optional" priority="0" order="30" xbrldt:contextElement="segment"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/srt/2020/elts/srt-2020-01-31.xsd#srt_RangeMember" xlink:label="locator_srt_RangeMember_5883ec0b-1f63-cfd6-de3f-2a5c1a8fb772_default"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="locator_srt_RangeAxis" xlink:to="locator_srt_RangeMember_5883ec0b-1f63-cfd6-de3f-2a5c1a8fb772_default" use="optional" priority="0" order="30" xbrldt:contextElement="segment"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_BusinessAcquisitionAcquireeDomain" xlink:label="locator_us-gaap_BusinessAcquisitionAcquireeDomain_4a19e3a2-4c46-35d6-f929-d19f6525fbfb_default"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="locator_us-gaap_BusinessAcquisitionAxis" xlink:to="locator_us-gaap_BusinessAcquisitionAcquireeDomain_4a19e3a2-4c46-35d6-f929-d19f6525fbfb_default" use="optional" priority="0" order="30" xbrldt:contextElement="segment"/>
  </definitionLink>
  <definitionLink xlink:type="extended" xlink:role="http://cassinfo.com/role/cass-aiasoiad">
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_AcquiredFiniteLivedIntangibleAssetsLineItems" xlink:label="locator_us-gaap_AcquiredFiniteLivedIntangibleAssetsLineItems"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_AdjustmentForAmortizationAbstract" xlink:label="locator_us-gaap_AdjustmentForAmortizationAbstract"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_AcquiredFiniteLivedIntangibleAssetsLineItems" xlink:to="locator_us-gaap_AdjustmentForAmortizationAbstract" use="optional" priority="0" order="0"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsGross" xlink:label="locator_us-gaap_FiniteLivedIntangibleAssetsGross"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_AdjustmentForAmortizationAbstract" xlink:to="locator_us-gaap_FiniteLivedIntangibleAssetsGross" use="optional" priority="0" order="1"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization" xlink:label="locator_us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_AdjustmentForAmortizationAbstract" xlink:to="locator_us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization" use="optional" priority="0" order="2"/>
    <loc xlink:type="locator" xlink:href="cass-20201231.xsd#cass_UnamortizedIntangibleAssetAbstract" xlink:label="locator_cass_UnamortizedIntangibleAssetAbstract"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_AcquiredFiniteLivedIntangibleAssetsLineItems" xlink:to="locator_cass_UnamortizedIntangibleAssetAbstract" use="optional" priority="0" order="3"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_GoodwillGross" xlink:label="locator_us-gaap_GoodwillGross"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_cass_UnamortizedIntangibleAssetAbstract" xlink:to="locator_us-gaap_GoodwillGross" use="optional" priority="0" order="4"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_GoodwillImpairedAccumulatedImpairmentLoss" xlink:label="locator_us-gaap_GoodwillImpairedAccumulatedImpairmentLoss"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_cass_UnamortizedIntangibleAssetAbstract" xlink:to="locator_us-gaap_GoodwillImpairedAccumulatedImpairmentLoss" use="optional" priority="0" order="5"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_IntangibleAssetsNetIncludingGoodwill" xlink:label="locator_us-gaap_IntangibleAssetsNetIncludingGoodwill"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_AcquiredFiniteLivedIntangibleAssetsLineItems" xlink:to="locator_us-gaap_IntangibleAssetsNetIncludingGoodwill" use="optional" priority="0" order="6"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ScheduleOfAcquiredFiniteLivedIntangibleAssetByMajorClassTable" xlink:label="locator_us-gaap_ScheduleOfAcquiredFiniteLivedIntangibleAssetByMajorClassTable"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="locator_us-gaap_AcquiredFiniteLivedIntangibleAssetsLineItems" xlink:to="locator_us-gaap_ScheduleOfAcquiredFiniteLivedIntangibleAssetByMajorClassTable" use="optional" priority="0" order="10" xbrldt:contextElement="segment" xbrldt:closed="true"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis" xlink:label="locator_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="locator_us-gaap_ScheduleOfAcquiredFiniteLivedIntangibleAssetByMajorClassTable" xlink:to="locator_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis" use="optional" priority="0" order="1"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain" xlink:label="locator_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="locator_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis" xlink:to="locator_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain" use="optional" priority="0" order="20"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_CustomerListsMember" xlink:label="locator_us-gaap_CustomerListsMember"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain" xlink:to="locator_us-gaap_CustomerListsMember" use="optional" priority="0" order="11"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_PatentsMember" xlink:label="locator_us-gaap_PatentsMember"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain" xlink:to="locator_us-gaap_PatentsMember" use="optional" priority="0" order="21"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_NoncompeteAgreementsMember" xlink:label="locator_us-gaap_NoncompeteAgreementsMember"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain" xlink:to="locator_us-gaap_NoncompeteAgreementsMember" use="optional" priority="0" order="31"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ComputerSoftwareIntangibleAssetMember" xlink:label="locator_us-gaap_ComputerSoftwareIntangibleAssetMember"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain" xlink:to="locator_us-gaap_ComputerSoftwareIntangibleAssetMember" use="optional" priority="0" order="41"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_TradeNamesMember" xlink:label="locator_us-gaap_TradeNamesMember"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain" xlink:to="locator_us-gaap_TradeNamesMember" use="optional" priority="0" order="51"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_OtherIntangibleAssetsMember" xlink:label="locator_us-gaap_OtherIntangibleAssetsMember"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain" xlink:to="locator_us-gaap_OtherIntangibleAssetsMember" use="optional" priority="0" order="61"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain" xlink:label="locator_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_39ea7613-8689-cf2f-ddc9-ea36481583ab_default"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="locator_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis" xlink:to="locator_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_39ea7613-8689-cf2f-ddc9-ea36481583ab_default" use="optional" priority="0" order="30" xbrldt:contextElement="segment"/>
  </definitionLink>
  <definitionLink xlink:type="extended" xlink:role="http://cassinfo.com/role/UnusedAvailableLinesOfCreditDetails">
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_LineOfCreditFacilityLineItems" xlink:label="locator_us-gaap_LineOfCreditFacilityLineItems"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity" xlink:label="locator_us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_LineOfCreditFacilityLineItems" xlink:to="locator_us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity" use="optional" priority="0" order="0"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_LineOfCredit" xlink:label="locator_us-gaap_LineOfCredit"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_LineOfCreditFacilityLineItems" xlink:to="locator_us-gaap_LineOfCredit" use="optional" priority="0" order="1"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_LineOfCreditFacilityTable" xlink:label="locator_us-gaap_LineOfCreditFacilityTable"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="locator_us-gaap_LineOfCreditFacilityLineItems" xlink:to="locator_us-gaap_LineOfCreditFacilityTable" use="optional" priority="0" order="10" xbrldt:contextElement="segment" xbrldt:closed="true"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_LongtermDebtTypeAxis" xlink:label="locator_us-gaap_LongtermDebtTypeAxis"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="locator_us-gaap_LineOfCreditFacilityTable" xlink:to="locator_us-gaap_LongtermDebtTypeAxis" use="optional" priority="0" order="1"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_LongtermDebtTypeDomain" xlink:label="locator_us-gaap_LongtermDebtTypeDomain"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="locator_us-gaap_LongtermDebtTypeAxis" xlink:to="locator_us-gaap_LongtermDebtTypeDomain" use="optional" priority="0" order="20"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_UnsecuredDebtMember" xlink:label="locator_us-gaap_UnsecuredDebtMember"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_LongtermDebtTypeDomain" xlink:to="locator_us-gaap_UnsecuredDebtMember" use="optional" priority="0" order="1"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_SecuredDebtMember" xlink:label="locator_us-gaap_SecuredDebtMember"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_LongtermDebtTypeDomain" xlink:to="locator_us-gaap_SecuredDebtMember" use="optional" priority="0" order="71"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_LineOfCreditFacilityAxis" xlink:label="locator_us-gaap_LineOfCreditFacilityAxis"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="locator_us-gaap_LineOfCreditFacilityTable" xlink:to="locator_us-gaap_LineOfCreditFacilityAxis" use="optional" priority="0" order="2"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_LineOfCreditFacilityLenderDomain" xlink:label="locator_us-gaap_LineOfCreditFacilityLenderDomain"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="locator_us-gaap_LineOfCreditFacilityAxis" xlink:to="locator_us-gaap_LineOfCreditFacilityLenderDomain" use="optional" priority="0" order="20"/>
    <loc xlink:type="locator" xlink:href="cass-20201231.xsd#cass_UsBankMember" xlink:label="locator_cass_UsBankMember"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_LineOfCreditFacilityLenderDomain" xlink:to="locator_cass_UsBankMember" use="optional" priority="0" order="12"/>
    <loc xlink:type="locator" xlink:href="cass-20201231.xsd#cass_UmbBankMember" xlink:label="locator_cass_UmbBankMember"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_LineOfCreditFacilityLenderDomain" xlink:to="locator_cass_UmbBankMember" use="optional" priority="0" order="22"/>
    <loc xlink:type="locator" xlink:href="cass-20201231.xsd#cass_WellsFargoBankMember" xlink:label="locator_cass_WellsFargoBankMember"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_LineOfCreditFacilityLenderDomain" xlink:to="locator_cass_WellsFargoBankMember" use="optional" priority="0" order="32"/>
    <loc xlink:type="locator" xlink:href="cass-20201231.xsd#cass_PncBankMember" xlink:label="locator_cass_PncBankMember"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_LineOfCreditFacilityLenderDomain" xlink:to="locator_cass_PncBankMember" use="optional" priority="0" order="42"/>
    <loc xlink:type="locator" xlink:href="cass-20201231.xsd#cass_FrostNationalBankMember" xlink:label="locator_cass_FrostNationalBankMember"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_LineOfCreditFacilityLenderDomain" xlink:to="locator_cass_FrostNationalBankMember" use="optional" priority="0" order="52"/>
    <loc xlink:type="locator" xlink:href="cass-20201231.xsd#cass_JpmChaseBankMember" xlink:label="locator_cass_JpmChaseBankMember"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_LineOfCreditFacilityLenderDomain" xlink:to="locator_cass_JpmChaseBankMember" use="optional" priority="0" order="62"/>
    <loc xlink:type="locator" xlink:href="cass-20201231.xsd#cass_FederalHomeLoanBankMember" xlink:label="locator_cass_FederalHomeLoanBankMember"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_LineOfCreditFacilityLenderDomain" xlink:to="locator_cass_FederalHomeLoanBankMember" use="optional" priority="0" order="72"/>
    <loc xlink:type="locator" xlink:href="cass-20201231.xsd#cass_FirstTennesseeBankMember" xlink:label="locator_cass_FirstTennesseeBankMember"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_LineOfCreditFacilityLenderDomain" xlink:to="locator_cass_FirstTennesseeBankMember" use="optional" priority="0" order="92"/>
    <loc xlink:type="locator" xlink:href="cass-20201231.xsd#cass_PPPMember" xlink:label="locator_cass_PPPMember"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_LineOfCreditFacilityLenderDomain" xlink:to="locator_cass_PPPMember" use="optional" priority="0" order="122"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_LongtermDebtTypeDomain" xlink:label="locator_us-gaap_LongtermDebtTypeDomain_3da77b2a-1c2e-220a-f3d2-a8c654b14887_default"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="locator_us-gaap_LongtermDebtTypeAxis" xlink:to="locator_us-gaap_LongtermDebtTypeDomain_3da77b2a-1c2e-220a-f3d2-a8c654b14887_default" use="optional" priority="0" order="30" xbrldt:contextElement="segment"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_LineOfCreditFacilityLenderDomain" xlink:label="locator_us-gaap_LineOfCreditFacilityLenderDomain_b30ecee3-4934-5a8c-613a-889b68452fc4_default"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="locator_us-gaap_LineOfCreditFacilityAxis" xlink:to="locator_us-gaap_LineOfCreditFacilityLenderDomain_b30ecee3-4934-5a8c-613a-889b68452fc4_default" use="optional" priority="0" order="30" xbrldt:contextElement="segment"/>
  </definitionLink>
  <definitionLink xlink:type="extended" xlink:role="http://cassinfo.com/role/EmployeeBenefitPlansNarrativeDetails">
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DefinedBenefitPlanDisclosureLineItems" xlink:label="locator_us-gaap_DefinedBenefitPlanDisclosureLineItems"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DefinedBenefitPlanAccumulatedBenefitObligation" xlink:label="locator_us-gaap_DefinedBenefitPlanAccumulatedBenefitObligation"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_DefinedBenefitPlanDisclosureLineItems" xlink:to="locator_us-gaap_DefinedBenefitPlanAccumulatedBenefitObligation" use="optional" priority="0" order="0"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_PensionContributions" xlink:label="locator_us-gaap_PensionContributions"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_DefinedBenefitPlanDisclosureLineItems" xlink:to="locator_us-gaap_PensionContributions" use="optional" priority="0" order="1"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DefinedBenefitPlanPlanAssetsTargetAllocationPercentage" xlink:label="locator_us-gaap_DefinedBenefitPlanPlanAssetsTargetAllocationPercentage"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_DefinedBenefitPlanDisclosureLineItems" xlink:to="locator_us-gaap_DefinedBenefitPlanPlanAssetsTargetAllocationPercentage" use="optional" priority="0" order="2"/>
    <loc xlink:type="locator" xlink:href="cass-20201231.xsd#cass_DefinedBenefitPlanLongTermRateOfReturnOnAssetsExpectedRange" xlink:label="locator_cass_DefinedBenefitPlanLongTermRateOfReturnOnAssetsExpectedRange"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_DefinedBenefitPlanDisclosureLineItems" xlink:to="locator_cass_DefinedBenefitPlanLongTermRateOfReturnOnAssetsExpectedRange" use="optional" priority="0" order="3"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_PensionExpense" xlink:label="locator_us-gaap_PensionExpense"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_DefinedBenefitPlanDisclosureLineItems" xlink:to="locator_us-gaap_PensionExpense" use="optional" priority="0" order="4"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DefinedBenefitPlanExpectedFutureEmployerContributionsRemainderOfFiscalYear" xlink:label="locator_us-gaap_DefinedBenefitPlanExpectedFutureEmployerContributionsRemainderOfFiscalYear"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_DefinedBenefitPlanDisclosureLineItems" xlink:to="locator_us-gaap_DefinedBenefitPlanExpectedFutureEmployerContributionsRemainderOfFiscalYear" use="optional" priority="0" order="5"/>
    <loc xlink:type="locator" xlink:href="cass-20201231.xsd#cass_PeriodForExpectedFutureBenefitsPayable" xlink:label="locator_cass_PeriodForExpectedFutureBenefitsPayable"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_DefinedBenefitPlanDisclosureLineItems" xlink:to="locator_cass_PeriodForExpectedFutureBenefitsPayable" use="optional" priority="0" order="6"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DefinedBenefitPlanPlanAssetsBenefitsPaid" xlink:label="locator_us-gaap_DefinedBenefitPlanPlanAssetsBenefitsPaid"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_DefinedBenefitPlanDisclosureLineItems" xlink:to="locator_us-gaap_DefinedBenefitPlanPlanAssetsBenefitsPaid" use="optional" priority="0" order="7"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DefinedBenefitPlanExpectedAmortizationOfPriorServiceCostCreditNextFiscalYear" xlink:label="locator_us-gaap_DefinedBenefitPlanExpectedAmortizationOfPriorServiceCostCreditNextFiscalYear"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_DefinedBenefitPlanDisclosureLineItems" xlink:to="locator_us-gaap_DefinedBenefitPlanExpectedAmortizationOfPriorServiceCostCreditNextFiscalYear" use="optional" priority="0" order="8"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DefinedBenefitPlanAmortizationOfGainsLosses" xlink:label="locator_us-gaap_DefinedBenefitPlanAmortizationOfGainsLosses"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_DefinedBenefitPlanDisclosureLineItems" xlink:to="locator_us-gaap_DefinedBenefitPlanAmortizationOfGainsLosses" use="optional" priority="0" order="9"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ScheduleOfDefinedBenefitPlansDisclosuresTable" xlink:label="locator_us-gaap_ScheduleOfDefinedBenefitPlansDisclosuresTable"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="locator_us-gaap_DefinedBenefitPlanDisclosureLineItems" xlink:to="locator_us-gaap_ScheduleOfDefinedBenefitPlansDisclosuresTable" use="optional" priority="0" order="10" xbrldt:contextElement="segment" xbrldt:closed="true"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_RetirementPlanTypeAxis" xlink:label="locator_us-gaap_RetirementPlanTypeAxis"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="locator_us-gaap_ScheduleOfDefinedBenefitPlansDisclosuresTable" xlink:to="locator_us-gaap_RetirementPlanTypeAxis" use="optional" priority="0" order="1"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_RetirementPlanTypeDomain" xlink:label="locator_us-gaap_RetirementPlanTypeDomain"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="locator_us-gaap_RetirementPlanTypeAxis" xlink:to="locator_us-gaap_RetirementPlanTypeDomain" use="optional" priority="0" order="20"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_PensionPlansDefinedBenefitMember" xlink:label="locator_us-gaap_PensionPlansDefinedBenefitMember"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_RetirementPlanTypeDomain" xlink:to="locator_us-gaap_PensionPlansDefinedBenefitMember" use="optional" priority="0" order="1"/>
    <loc xlink:type="locator" xlink:href="cass-20201231.xsd#cass_SupplementalExecutiveRetirementPlanMember" xlink:label="locator_cass_SupplementalExecutiveRetirementPlanMember"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_RetirementPlanTypeDomain" xlink:to="locator_cass_SupplementalExecutiveRetirementPlanMember" use="optional" priority="0" order="101"/>
    <loc xlink:type="locator" xlink:href="cass-20201231.xsd#cass_NoncontributoryProfitSharingProgramMember" xlink:label="locator_cass_NoncontributoryProfitSharingProgramMember"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_RetirementPlanTypeDomain" xlink:to="locator_cass_NoncontributoryProfitSharingProgramMember" use="optional" priority="0" order="161"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis" xlink:label="locator_us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="locator_us-gaap_ScheduleOfDefinedBenefitPlansDisclosuresTable" xlink:to="locator_us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis" use="optional" priority="0" order="2"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_PlanAssetCategoriesDomain" xlink:label="locator_us-gaap_PlanAssetCategoriesDomain"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="locator_us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis" xlink:to="locator_us-gaap_PlanAssetCategoriesDomain" use="optional" priority="0" order="20"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FixedIncomeFundsMember" xlink:label="locator_us-gaap_FixedIncomeFundsMember"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_PlanAssetCategoriesDomain" xlink:to="locator_us-gaap_FixedIncomeFundsMember" use="optional" priority="0" order="21"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_EquitySecuritiesMember" xlink:label="locator_us-gaap_EquitySecuritiesMember"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_PlanAssetCategoriesDomain" xlink:to="locator_us-gaap_EquitySecuritiesMember" use="optional" priority="0" order="31"/>
    <loc xlink:type="locator" xlink:href="cass-20201231.xsd#cass_ForeignEquitySecuritiesMember" xlink:label="locator_cass_ForeignEquitySecuritiesMember"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_PlanAssetCategoriesDomain" xlink:to="locator_cass_ForeignEquitySecuritiesMember" use="optional" priority="0" order="41"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_SubsequentEventTypeAxis" xlink:label="locator_us-gaap_SubsequentEventTypeAxis"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="locator_us-gaap_ScheduleOfDefinedBenefitPlansDisclosuresTable" xlink:to="locator_us-gaap_SubsequentEventTypeAxis" use="optional" priority="0" order="3"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_SubsequentEventTypeDomain" xlink:label="locator_us-gaap_SubsequentEventTypeDomain"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="locator_us-gaap_SubsequentEventTypeAxis" xlink:to="locator_us-gaap_SubsequentEventTypeDomain" use="optional" priority="0" order="20"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_SubsequentEventMember" xlink:label="locator_us-gaap_SubsequentEventMember"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_SubsequentEventTypeDomain" xlink:to="locator_us-gaap_SubsequentEventMember" use="optional" priority="0" order="92"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DefinedContributionPlanEmployerDiscretionaryContributionAmount" xlink:label="locator_us-gaap_DefinedContributionPlanEmployerDiscretionaryContributionAmount"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_DefinedBenefitPlanDisclosureLineItems" xlink:to="locator_us-gaap_DefinedContributionPlanEmployerDiscretionaryContributionAmount" use="optional" priority="0" order="10"/>
    <loc xlink:type="locator" xlink:href="cass-20201231.xsd#cass_ProfitSharingExpenseRecognizedInConsolidatedStatementsOfIncome" xlink:label="locator_cass_ProfitSharingExpenseRecognizedInConsolidatedStatementsOfIncome"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_DefinedBenefitPlanDisclosureLineItems" xlink:to="locator_cass_ProfitSharingExpenseRecognizedInConsolidatedStatementsOfIncome" use="optional" priority="0" order="11"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_RetirementPlanTypeDomain" xlink:label="locator_us-gaap_RetirementPlanTypeDomain_35bd028f-84ad-6fbd-f388-1a0ad0f38b12_default"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="locator_us-gaap_RetirementPlanTypeAxis" xlink:to="locator_us-gaap_RetirementPlanTypeDomain_35bd028f-84ad-6fbd-f388-1a0ad0f38b12_default" use="optional" priority="0" order="30" xbrldt:contextElement="segment"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_PlanAssetCategoriesDomain" xlink:label="locator_us-gaap_PlanAssetCategoriesDomain_4b876b42-788b-1eb7-24f6-d59827fc2aa3_default"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="locator_us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis" xlink:to="locator_us-gaap_PlanAssetCategoriesDomain_4b876b42-788b-1eb7-24f6-d59827fc2aa3_default" use="optional" priority="0" order="30" xbrldt:contextElement="segment"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_SubsequentEventTypeDomain" xlink:label="locator_us-gaap_SubsequentEventTypeDomain_50e83c77-5b82-4ffa-eb97-3524f03d5619_default"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="locator_us-gaap_SubsequentEventTypeAxis" xlink:to="locator_us-gaap_SubsequentEventTypeDomain_50e83c77-5b82-4ffa-eb97-3524f03d5619_default" use="optional" priority="0" order="30" xbrldt:contextElement="segment"/>
  </definitionLink>
  <definitionLink xlink:type="extended" xlink:role="http://cassinfo.com/role/cass-ebpsoautdtpbod">
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DefinedBenefitPlanDisclosureLineItems" xlink:label="locator_us-gaap_DefinedBenefitPlanDisclosureLineItems"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingBenefitObligationDiscountRate" xlink:label="locator_us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingBenefitObligationDiscountRate"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_DefinedBenefitPlanDisclosureLineItems" xlink:to="locator_us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingBenefitObligationDiscountRate" use="optional" priority="0" order="0"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingBenefitObligationRateOfCompensationIncrease" xlink:label="locator_us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingBenefitObligationRateOfCompensationIncrease"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_DefinedBenefitPlanDisclosureLineItems" xlink:to="locator_us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingBenefitObligationRateOfCompensationIncrease" use="optional" priority="0" order="1"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ScheduleOfDefinedBenefitPlansDisclosuresTable" xlink:label="locator_us-gaap_ScheduleOfDefinedBenefitPlansDisclosuresTable"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="locator_us-gaap_DefinedBenefitPlanDisclosureLineItems" xlink:to="locator_us-gaap_ScheduleOfDefinedBenefitPlansDisclosuresTable" use="optional" priority="0" order="10" xbrldt:contextElement="segment" xbrldt:closed="true"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_RetirementPlanTypeAxis" xlink:label="locator_us-gaap_RetirementPlanTypeAxis"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="locator_us-gaap_ScheduleOfDefinedBenefitPlansDisclosuresTable" xlink:to="locator_us-gaap_RetirementPlanTypeAxis" use="optional" priority="0" order="1"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_RetirementPlanTypeDomain" xlink:label="locator_us-gaap_RetirementPlanTypeDomain"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="locator_us-gaap_RetirementPlanTypeAxis" xlink:to="locator_us-gaap_RetirementPlanTypeDomain" use="optional" priority="0" order="20"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_PensionPlansDefinedBenefitMember" xlink:label="locator_us-gaap_PensionPlansDefinedBenefitMember"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_RetirementPlanTypeDomain" xlink:to="locator_us-gaap_PensionPlansDefinedBenefitMember" use="optional" priority="0" order="1"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_RetirementPlanTypeDomain" xlink:label="locator_us-gaap_RetirementPlanTypeDomain_a239d926-caf9-acf3-bb22-830fc812bf92_default"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="locator_us-gaap_RetirementPlanTypeAxis" xlink:to="locator_us-gaap_RetirementPlanTypeDomain_a239d926-caf9-acf3-bb22-830fc812bf92_default" use="optional" priority="0" order="30" xbrldt:contextElement="segment"/>
  </definitionLink>
  <definitionLink xlink:type="extended" xlink:role="http://cassinfo.com/role/cass-ebpsoppcd">
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DefinedBenefitPlanDisclosureLineItems" xlink:label="locator_us-gaap_DefinedBenefitPlanDisclosureLineItems"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DefinedBenefitPlanServiceCost" xlink:label="locator_us-gaap_DefinedBenefitPlanServiceCost"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_DefinedBenefitPlanDisclosureLineItems" xlink:to="locator_us-gaap_DefinedBenefitPlanServiceCost" use="optional" priority="0" order="0"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DefinedBenefitPlanInterestCost" xlink:label="locator_us-gaap_DefinedBenefitPlanInterestCost"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_DefinedBenefitPlanDisclosureLineItems" xlink:to="locator_us-gaap_DefinedBenefitPlanInterestCost" use="optional" priority="0" order="1"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DefinedBenefitPlanExpectedReturnOnPlanAssets" xlink:label="locator_us-gaap_DefinedBenefitPlanExpectedReturnOnPlanAssets"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_DefinedBenefitPlanDisclosureLineItems" xlink:to="locator_us-gaap_DefinedBenefitPlanExpectedReturnOnPlanAssets" use="optional" priority="0" order="2"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DefinedBenefitPlanAmortizationOfPriorServiceCostCredit" xlink:label="locator_us-gaap_DefinedBenefitPlanAmortizationOfPriorServiceCostCredit"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_DefinedBenefitPlanDisclosureLineItems" xlink:to="locator_us-gaap_DefinedBenefitPlanAmortizationOfPriorServiceCostCredit" use="optional" priority="0" order="3"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DefinedBenefitPlanNetPeriodicBenefitCost" xlink:label="locator_us-gaap_DefinedBenefitPlanNetPeriodicBenefitCost"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_DefinedBenefitPlanDisclosureLineItems" xlink:to="locator_us-gaap_DefinedBenefitPlanNetPeriodicBenefitCost" use="optional" priority="0" order="4"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ScheduleOfDefinedBenefitPlansDisclosuresTable" xlink:label="locator_us-gaap_ScheduleOfDefinedBenefitPlansDisclosuresTable"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="locator_us-gaap_DefinedBenefitPlanDisclosureLineItems" xlink:to="locator_us-gaap_ScheduleOfDefinedBenefitPlansDisclosuresTable" use="optional" priority="0" order="10" xbrldt:contextElement="segment" xbrldt:closed="true"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_RetirementPlanTypeAxis" xlink:label="locator_us-gaap_RetirementPlanTypeAxis"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="locator_us-gaap_ScheduleOfDefinedBenefitPlansDisclosuresTable" xlink:to="locator_us-gaap_RetirementPlanTypeAxis" use="optional" priority="0" order="1"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_RetirementPlanTypeDomain" xlink:label="locator_us-gaap_RetirementPlanTypeDomain"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="locator_us-gaap_RetirementPlanTypeAxis" xlink:to="locator_us-gaap_RetirementPlanTypeDomain" use="optional" priority="0" order="20"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_PensionPlansDefinedBenefitMember" xlink:label="locator_us-gaap_PensionPlansDefinedBenefitMember"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_RetirementPlanTypeDomain" xlink:to="locator_us-gaap_PensionPlansDefinedBenefitMember" use="optional" priority="0" order="1"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_RetirementPlanTypeDomain" xlink:label="locator_us-gaap_RetirementPlanTypeDomain_7db8240f-7092-ea85-e1b9-f532c4acf2c7_default"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="locator_us-gaap_RetirementPlanTypeAxis" xlink:to="locator_us-gaap_RetirementPlanTypeDomain_7db8240f-7092-ea85-e1b9-f532c4acf2c7_default" use="optional" priority="0" order="30" xbrldt:contextElement="segment"/>
  </definitionLink>
  <definitionLink xlink:type="extended" xlink:role="http://cassinfo.com/role/cass-ebpsoltroroad">
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DefinedBenefitPlanDisclosureLineItems" xlink:label="locator_us-gaap_DefinedBenefitPlanDisclosureLineItems"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DefinedBenefitPlanPlanAssetsTargetAllocationPercentage" xlink:label="locator_us-gaap_DefinedBenefitPlanPlanAssetsTargetAllocationPercentage"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_DefinedBenefitPlanDisclosureLineItems" xlink:to="locator_us-gaap_DefinedBenefitPlanPlanAssetsTargetAllocationPercentage" use="optional" priority="0" order="0"/>
    <loc xlink:type="locator" xlink:href="cass-20201231.xsd#cass_OneYearNominalReturn" xlink:label="locator_cass_OneYearNominalReturn"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_DefinedBenefitPlanDisclosureLineItems" xlink:to="locator_cass_OneYearNominalReturn" use="optional" priority="0" order="1"/>
    <loc xlink:type="locator" xlink:href="cass-20201231.xsd#cass_AnnualStandardDeviation" xlink:label="locator_cass_AnnualStandardDeviation"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_DefinedBenefitPlanDisclosureLineItems" xlink:to="locator_cass_AnnualStandardDeviation" use="optional" priority="0" order="2"/>
    <loc xlink:type="locator" xlink:href="cass-20201231.xsd#cass_ExpectedLongTermRateReturn" xlink:label="locator_cass_ExpectedLongTermRateReturn"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_DefinedBenefitPlanDisclosureLineItems" xlink:to="locator_cass_ExpectedLongTermRateReturn" use="optional" priority="0" order="3"/>
    <loc xlink:type="locator" xlink:href="cass-20201231.xsd#cass_LongTermRateOfReturnAllocation" xlink:label="locator_cass_LongTermRateOfReturnAllocation"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_DefinedBenefitPlanDisclosureLineItems" xlink:to="locator_cass_LongTermRateOfReturnAllocation" use="optional" priority="0" order="4"/>
    <loc xlink:type="locator" xlink:href="cass-20201231.xsd#cass_LongTermRateOfReturnAssumption" xlink:label="locator_cass_LongTermRateOfReturnAssumption"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_DefinedBenefitPlanDisclosureLineItems" xlink:to="locator_cass_LongTermRateOfReturnAssumption" use="optional" priority="0" order="5"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ScheduleOfDefinedBenefitPlansDisclosuresTable" xlink:label="locator_us-gaap_ScheduleOfDefinedBenefitPlansDisclosuresTable"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="locator_us-gaap_DefinedBenefitPlanDisclosureLineItems" xlink:to="locator_us-gaap_ScheduleOfDefinedBenefitPlansDisclosuresTable" use="optional" priority="0" order="10" xbrldt:contextElement="segment" xbrldt:closed="true"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis" xlink:label="locator_us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="locator_us-gaap_ScheduleOfDefinedBenefitPlansDisclosuresTable" xlink:to="locator_us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis" use="optional" priority="0" order="1"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_PlanAssetCategoriesDomain" xlink:label="locator_us-gaap_PlanAssetCategoriesDomain"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="locator_us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis" xlink:to="locator_us-gaap_PlanAssetCategoriesDomain" use="optional" priority="0" order="20"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FixedIncomeFundsMember" xlink:label="locator_us-gaap_FixedIncomeFundsMember"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_PlanAssetCategoriesDomain" xlink:to="locator_us-gaap_FixedIncomeFundsMember" use="optional" priority="0" order="1"/>
    <loc xlink:type="locator" xlink:href="cass-20201231.xsd#cass_EquitySecuritiesLargeCapMember" xlink:label="locator_cass_EquitySecuritiesLargeCapMember"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_PlanAssetCategoriesDomain" xlink:to="locator_cass_EquitySecuritiesLargeCapMember" use="optional" priority="0" order="11"/>
    <loc xlink:type="locator" xlink:href="cass-20201231.xsd#cass_EquitySecuritiesSmallCapMember" xlink:label="locator_cass_EquitySecuritiesSmallCapMember"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_PlanAssetCategoriesDomain" xlink:to="locator_cass_EquitySecuritiesSmallCapMember" use="optional" priority="0" order="21"/>
    <loc xlink:type="locator" xlink:href="cass-20201231.xsd#cass_ForeignEquitySecuritiesDevelopedMember" xlink:label="locator_cass_ForeignEquitySecuritiesDevelopedMember"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_PlanAssetCategoriesDomain" xlink:to="locator_cass_ForeignEquitySecuritiesDevelopedMember" use="optional" priority="0" order="31"/>
    <loc xlink:type="locator" xlink:href="cass-20201231.xsd#cass_ForeignEquitySecuritiesEmergingMember" xlink:label="locator_cass_ForeignEquitySecuritiesEmergingMember"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_PlanAssetCategoriesDomain" xlink:to="locator_cass_ForeignEquitySecuritiesEmergingMember" use="optional" priority="0" order="41"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_PlanAssetCategoriesDomain" xlink:label="locator_us-gaap_PlanAssetCategoriesDomain_a63d30c2-1bb0-8baa-745e-1c033c6e26e2_default"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="locator_us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis" xlink:to="locator_us-gaap_PlanAssetCategoriesDomain_a63d30c2-1bb0-8baa-745e-1c033c6e26e2_default" use="optional" priority="0" order="30" xbrldt:contextElement="segment"/>
  </definitionLink>
  <definitionLink xlink:type="extended" xlink:role="http://cassinfo.com/role/cass-ebpsotfvmbtoad">
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DefinedBenefitPlanDisclosureLineItems" xlink:label="locator_us-gaap_DefinedBenefitPlanDisclosureLineItems"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DefinedBenefitPlanFairValueOfPlanAssets" xlink:label="locator_us-gaap_DefinedBenefitPlanFairValueOfPlanAssets"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_DefinedBenefitPlanDisclosureLineItems" xlink:to="locator_us-gaap_DefinedBenefitPlanFairValueOfPlanAssets" use="optional" priority="0" order="0"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ScheduleOfDefinedBenefitPlansDisclosuresTable" xlink:label="locator_us-gaap_ScheduleOfDefinedBenefitPlansDisclosuresTable"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="locator_us-gaap_DefinedBenefitPlanDisclosureLineItems" xlink:to="locator_us-gaap_ScheduleOfDefinedBenefitPlansDisclosuresTable" use="optional" priority="0" order="10" xbrldt:contextElement="segment" xbrldt:closed="true"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis" xlink:label="locator_us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="locator_us-gaap_ScheduleOfDefinedBenefitPlansDisclosuresTable" xlink:to="locator_us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis" use="optional" priority="0" order="1"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_PlanAssetCategoriesDomain" xlink:label="locator_us-gaap_PlanAssetCategoriesDomain"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="locator_us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis" xlink:to="locator_us-gaap_PlanAssetCategoriesDomain" use="optional" priority="0" order="20"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_CashAndCashEquivalentsMember" xlink:label="locator_us-gaap_CashAndCashEquivalentsMember"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_PlanAssetCategoriesDomain" xlink:to="locator_us-gaap_CashAndCashEquivalentsMember" use="optional" priority="0" order="11"/>
    <loc xlink:type="locator" xlink:href="cass-20201231.xsd#cass_UnitedStatesLargeCapGrowthMember" xlink:label="locator_cass_UnitedStatesLargeCapGrowthMember"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_PlanAssetCategoriesDomain" xlink:to="locator_cass_UnitedStatesLargeCapGrowthMember" use="optional" priority="0" order="21"/>
    <loc xlink:type="locator" xlink:href="cass-20201231.xsd#cass_UnitedStatesSmallAndMidCapGrowthMember" xlink:label="locator_cass_UnitedStatesSmallAndMidCapGrowthMember"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_PlanAssetCategoriesDomain" xlink:to="locator_cass_UnitedStatesSmallAndMidCapGrowthMember" use="optional" priority="0" order="31"/>
    <loc xlink:type="locator" xlink:href="cass-20201231.xsd#cass_NonUnitedStatesCoreMember" xlink:label="locator_cass_NonUnitedStatesCoreMember"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_PlanAssetCategoriesDomain" xlink:to="locator_cass_NonUnitedStatesCoreMember" use="optional" priority="0" order="41"/>
    <loc xlink:type="locator" xlink:href="cass-20201231.xsd#cass_UnitedStatesLargeCapPassiveMember" xlink:label="locator_cass_UnitedStatesLargeCapPassiveMember"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_PlanAssetCategoriesDomain" xlink:to="locator_cass_UnitedStatesLargeCapPassiveMember" use="optional" priority="0" order="51"/>
    <loc xlink:type="locator" xlink:href="cass-20201231.xsd#cass_EmergingMarketsMember" xlink:label="locator_cass_EmergingMarketsMember"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_PlanAssetCategoriesDomain" xlink:to="locator_cass_EmergingMarketsMember" use="optional" priority="0" order="61"/>
    <loc xlink:type="locator" xlink:href="cass-20201231.xsd#cass_UnitedStatesCoreOpportunisticMember" xlink:label="locator_cass_UnitedStatesCoreOpportunisticMember"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_PlanAssetCategoriesDomain" xlink:to="locator_cass_UnitedStatesCoreOpportunisticMember" use="optional" priority="0" order="71"/>
    <loc xlink:type="locator" xlink:href="cass-20201231.xsd#cass_UnitedStatesPassiveMember" xlink:label="locator_cass_UnitedStatesPassiveMember"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_PlanAssetCategoriesDomain" xlink:to="locator_cass_UnitedStatesPassiveMember" use="optional" priority="0" order="81"/>
    <loc xlink:type="locator" xlink:href="cass-20201231.xsd#cass_OpportunisticMember" xlink:label="locator_cass_OpportunisticMember"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_PlanAssetCategoriesDomain" xlink:to="locator_cass_OpportunisticMember" use="optional" priority="0" order="91"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FairValueByFairValueHierarchyLevelAxis" xlink:label="locator_us-gaap_FairValueByFairValueHierarchyLevelAxis"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="locator_us-gaap_ScheduleOfDefinedBenefitPlansDisclosuresTable" xlink:to="locator_us-gaap_FairValueByFairValueHierarchyLevelAxis" use="optional" priority="0" order="2"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain" xlink:label="locator_us-gaap_FairValueMeasurementsFairValueHierarchyDomain"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="locator_us-gaap_FairValueByFairValueHierarchyLevelAxis" xlink:to="locator_us-gaap_FairValueMeasurementsFairValueHierarchyDomain" use="optional" priority="0" order="20"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FairValueInputsLevel1Member" xlink:label="locator_us-gaap_FairValueInputsLevel1Member"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_FairValueMeasurementsFairValueHierarchyDomain" xlink:to="locator_us-gaap_FairValueInputsLevel1Member" use="optional" priority="0" order="101"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FairValueInputsLevel2Member" xlink:label="locator_us-gaap_FairValueInputsLevel2Member"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_FairValueMeasurementsFairValueHierarchyDomain" xlink:to="locator_us-gaap_FairValueInputsLevel2Member" use="optional" priority="0" order="201"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_PlanAssetCategoriesDomain" xlink:label="locator_us-gaap_PlanAssetCategoriesDomain_9118d21d-3dc2-f14d-00f3-2e96dcbb0445_default"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="locator_us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis" xlink:to="locator_us-gaap_PlanAssetCategoriesDomain_9118d21d-3dc2-f14d-00f3-2e96dcbb0445_default" use="optional" priority="0" order="30" xbrldt:contextElement="segment"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain" xlink:label="locator_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_5559a7ef-077b-4a52-1b68-fbffc8c82416_default"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="locator_us-gaap_FairValueByFairValueHierarchyLevelAxis" xlink:to="locator_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_5559a7ef-077b-4a52-1b68-fbffc8c82416_default" use="optional" priority="0" order="30" xbrldt:contextElement="segment"/>
  </definitionLink>
  <definitionLink xlink:type="extended" xlink:role="http://cassinfo.com/role/cass-ebpsotaitspbod">
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DefinedBenefitPlanDisclosureLineItems" xlink:label="locator_us-gaap_DefinedBenefitPlanDisclosureLineItems"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DefinedBenefitPlanChangeInBenefitObligationRollForward" xlink:label="locator_us-gaap_DefinedBenefitPlanChangeInBenefitObligationRollForward"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_DefinedBenefitPlanDisclosureLineItems" xlink:to="locator_us-gaap_DefinedBenefitPlanChangeInBenefitObligationRollForward" use="optional" priority="0" order="0"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DefinedBenefitPlanBenefitObligation" xlink:label="locator_us-gaap_DefinedBenefitPlanBenefitObligation"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_DefinedBenefitPlanChangeInBenefitObligationRollForward" xlink:to="locator_us-gaap_DefinedBenefitPlanBenefitObligation" use="optional" priority="0" order="1"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DefinedBenefitPlanServiceCost" xlink:label="locator_us-gaap_DefinedBenefitPlanServiceCost"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_DefinedBenefitPlanChangeInBenefitObligationRollForward" xlink:to="locator_us-gaap_DefinedBenefitPlanServiceCost" use="optional" priority="0" order="2"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DefinedBenefitPlanInterestCost" xlink:label="locator_us-gaap_DefinedBenefitPlanInterestCost"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_DefinedBenefitPlanChangeInBenefitObligationRollForward" xlink:to="locator_us-gaap_DefinedBenefitPlanInterestCost" use="optional" priority="0" order="3"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DefinedBenefitPlanPlanAssetsBenefitsPaid" xlink:label="locator_us-gaap_DefinedBenefitPlanPlanAssetsBenefitsPaid"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_DefinedBenefitPlanChangeInBenefitObligationRollForward" xlink:to="locator_us-gaap_DefinedBenefitPlanPlanAssetsBenefitsPaid" use="optional" priority="0" order="4"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DefinedBenefitPlanActuarialGainLoss" xlink:label="locator_us-gaap_DefinedBenefitPlanActuarialGainLoss"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_DefinedBenefitPlanChangeInBenefitObligationRollForward" xlink:to="locator_us-gaap_DefinedBenefitPlanActuarialGainLoss" use="optional" priority="0" order="5"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ScheduleOfDefinedBenefitPlansDisclosuresTable" xlink:label="locator_us-gaap_ScheduleOfDefinedBenefitPlansDisclosuresTable"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="locator_us-gaap_DefinedBenefitPlanDisclosureLineItems" xlink:to="locator_us-gaap_ScheduleOfDefinedBenefitPlansDisclosuresTable" use="optional" priority="0" order="10" xbrldt:contextElement="segment" xbrldt:closed="true"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_RetirementPlanTypeAxis" xlink:label="locator_us-gaap_RetirementPlanTypeAxis"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="locator_us-gaap_ScheduleOfDefinedBenefitPlansDisclosuresTable" xlink:to="locator_us-gaap_RetirementPlanTypeAxis" use="optional" priority="0" order="1"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_RetirementPlanTypeDomain" xlink:label="locator_us-gaap_RetirementPlanTypeDomain"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="locator_us-gaap_RetirementPlanTypeAxis" xlink:to="locator_us-gaap_RetirementPlanTypeDomain" use="optional" priority="0" order="20"/>
    <loc xlink:type="locator" xlink:href="cass-20201231.xsd#cass_SupplementalExecutiveRetirementPlanMember" xlink:label="locator_cass_SupplementalExecutiveRetirementPlanMember"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_RetirementPlanTypeDomain" xlink:to="locator_cass_SupplementalExecutiveRetirementPlanMember" use="optional" priority="0" order="1"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_RetirementPlanTypeDomain" xlink:label="locator_us-gaap_RetirementPlanTypeDomain_90126c1b-d210-15c1-e812-e63f42cf9117_default"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="locator_us-gaap_RetirementPlanTypeAxis" xlink:to="locator_us-gaap_RetirementPlanTypeDomain_90126c1b-d210-15c1-e812-e63f42cf9117_default" use="optional" priority="0" order="30" xbrldt:contextElement="segment"/>
  </definitionLink>
  <definitionLink xlink:type="extended" xlink:role="http://cassinfo.com/role/cass-ebpsoautdpbootsd">
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DefinedBenefitPlanDisclosureLineItems" xlink:label="locator_us-gaap_DefinedBenefitPlanDisclosureLineItems"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingBenefitObligationDiscountRate" xlink:label="locator_us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingBenefitObligationDiscountRate"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_DefinedBenefitPlanDisclosureLineItems" xlink:to="locator_us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingBenefitObligationDiscountRate" use="optional" priority="0" order="0"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingBenefitObligationRateOfCompensationIncrease" xlink:label="locator_us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingBenefitObligationRateOfCompensationIncrease"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_DefinedBenefitPlanDisclosureLineItems" xlink:to="locator_us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingBenefitObligationRateOfCompensationIncrease" use="optional" priority="0" order="1"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ScheduleOfDefinedBenefitPlansDisclosuresTable" xlink:label="locator_us-gaap_ScheduleOfDefinedBenefitPlansDisclosuresTable"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="locator_us-gaap_DefinedBenefitPlanDisclosureLineItems" xlink:to="locator_us-gaap_ScheduleOfDefinedBenefitPlansDisclosuresTable" use="optional" priority="0" order="10" xbrldt:contextElement="segment" xbrldt:closed="true"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_RetirementPlanTypeAxis" xlink:label="locator_us-gaap_RetirementPlanTypeAxis"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="locator_us-gaap_ScheduleOfDefinedBenefitPlansDisclosuresTable" xlink:to="locator_us-gaap_RetirementPlanTypeAxis" use="optional" priority="0" order="1"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_RetirementPlanTypeDomain" xlink:label="locator_us-gaap_RetirementPlanTypeDomain"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="locator_us-gaap_RetirementPlanTypeAxis" xlink:to="locator_us-gaap_RetirementPlanTypeDomain" use="optional" priority="0" order="20"/>
    <loc xlink:type="locator" xlink:href="cass-20201231.xsd#cass_SupplementalExecutiveRetirementPlanMember" xlink:label="locator_cass_SupplementalExecutiveRetirementPlanMember"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_RetirementPlanTypeDomain" xlink:to="locator_cass_SupplementalExecutiveRetirementPlanMember" use="optional" priority="0" order="1"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_RetirementPlanTypeDomain" xlink:label="locator_us-gaap_RetirementPlanTypeDomain_8705b103-06ea-66c4-56dd-8cb3bc70455e_default"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="locator_us-gaap_RetirementPlanTypeAxis" xlink:to="locator_us-gaap_RetirementPlanTypeDomain_8705b103-06ea-66c4-56dd-8cb3bc70455e_default" use="optional" priority="0" order="30" xbrldt:contextElement="segment"/>
  </definitionLink>
  <definitionLink xlink:type="extended" xlink:role="http://cassinfo.com/role/EmployeeBenefitPlansScheduleOfExpectedFutureBenefitsPayableDetails">
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DefinedBenefitPlanDisclosureLineItems" xlink:label="locator_us-gaap_DefinedBenefitPlanDisclosureLineItems"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DefinedBenefitPlanExpectedFutureBenefitPaymentsNextTwelveMonths" xlink:label="locator_us-gaap_DefinedBenefitPlanExpectedFutureBenefitPaymentsNextTwelveMonths"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_DefinedBenefitPlanDisclosureLineItems" xlink:to="locator_us-gaap_DefinedBenefitPlanExpectedFutureBenefitPaymentsNextTwelveMonths" use="optional" priority="0" order="0"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DefinedBenefitPlanExpectedFutureBenefitPaymentsYearTwo" xlink:label="locator_us-gaap_DefinedBenefitPlanExpectedFutureBenefitPaymentsYearTwo"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_DefinedBenefitPlanDisclosureLineItems" xlink:to="locator_us-gaap_DefinedBenefitPlanExpectedFutureBenefitPaymentsYearTwo" use="optional" priority="0" order="1"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DefinedBenefitPlanExpectedFutureBenefitPaymentsYearThree" xlink:label="locator_us-gaap_DefinedBenefitPlanExpectedFutureBenefitPaymentsYearThree"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_DefinedBenefitPlanDisclosureLineItems" xlink:to="locator_us-gaap_DefinedBenefitPlanExpectedFutureBenefitPaymentsYearThree" use="optional" priority="0" order="2"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DefinedBenefitPlanExpectedFutureBenefitPaymentsYearFour" xlink:label="locator_us-gaap_DefinedBenefitPlanExpectedFutureBenefitPaymentsYearFour"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_DefinedBenefitPlanDisclosureLineItems" xlink:to="locator_us-gaap_DefinedBenefitPlanExpectedFutureBenefitPaymentsYearFour" use="optional" priority="0" order="3"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DefinedBenefitPlanExpectedFutureBenefitPaymentsYearFive" xlink:label="locator_us-gaap_DefinedBenefitPlanExpectedFutureBenefitPaymentsYearFive"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_DefinedBenefitPlanDisclosureLineItems" xlink:to="locator_us-gaap_DefinedBenefitPlanExpectedFutureBenefitPaymentsYearFive" use="optional" priority="0" order="4"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DefinedBenefitPlanExpectedFutureBenefitPaymentsFiveFiscalYearsThereafter" xlink:label="locator_us-gaap_DefinedBenefitPlanExpectedFutureBenefitPaymentsFiveFiscalYearsThereafter"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_DefinedBenefitPlanDisclosureLineItems" xlink:to="locator_us-gaap_DefinedBenefitPlanExpectedFutureBenefitPaymentsFiveFiscalYearsThereafter" use="optional" priority="0" order="5"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ScheduleOfDefinedBenefitPlansDisclosuresTable" xlink:label="locator_us-gaap_ScheduleOfDefinedBenefitPlansDisclosuresTable"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="locator_us-gaap_DefinedBenefitPlanDisclosureLineItems" xlink:to="locator_us-gaap_ScheduleOfDefinedBenefitPlansDisclosuresTable" use="optional" priority="0" order="10" xbrldt:contextElement="segment" xbrldt:closed="true"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_RetirementPlanTypeAxis" xlink:label="locator_us-gaap_RetirementPlanTypeAxis"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="locator_us-gaap_ScheduleOfDefinedBenefitPlansDisclosuresTable" xlink:to="locator_us-gaap_RetirementPlanTypeAxis" use="optional" priority="0" order="1"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_RetirementPlanTypeDomain" xlink:label="locator_us-gaap_RetirementPlanTypeDomain"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="locator_us-gaap_RetirementPlanTypeAxis" xlink:to="locator_us-gaap_RetirementPlanTypeDomain" use="optional" priority="0" order="20"/>
    <loc xlink:type="locator" xlink:href="cass-20201231.xsd#cass_SupplementalExecutiveRetirementPlanMember" xlink:label="locator_cass_SupplementalExecutiveRetirementPlanMember"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_RetirementPlanTypeDomain" xlink:to="locator_cass_SupplementalExecutiveRetirementPlanMember" use="optional" priority="0" order="1"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_RetirementPlanTypeDomain" xlink:label="locator_us-gaap_RetirementPlanTypeDomain_90d6ae57-aa3e-7416-52e5-34b8f94b3c45_default"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="locator_us-gaap_RetirementPlanTypeAxis" xlink:to="locator_us-gaap_RetirementPlanTypeDomain_90d6ae57-aa3e-7416-52e5-34b8f94b3c45_default" use="optional" priority="0" order="30" xbrldt:contextElement="segment"/>
  </definitionLink>
  <definitionLink xlink:type="extended" xlink:role="http://cassinfo.com/role/cass-ebpsospcd">
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DefinedBenefitPlanDisclosureLineItems" xlink:label="locator_us-gaap_DefinedBenefitPlanDisclosureLineItems"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DefinedBenefitPlanServiceCost" xlink:label="locator_us-gaap_DefinedBenefitPlanServiceCost"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_DefinedBenefitPlanDisclosureLineItems" xlink:to="locator_us-gaap_DefinedBenefitPlanServiceCost" use="optional" priority="0" order="0"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DefinedBenefitPlanInterestCost" xlink:label="locator_us-gaap_DefinedBenefitPlanInterestCost"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_DefinedBenefitPlanDisclosureLineItems" xlink:to="locator_us-gaap_DefinedBenefitPlanInterestCost" use="optional" priority="0" order="1"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DefinedBenefitPlanAmortizationOfPriorServiceCostCredit" xlink:label="locator_us-gaap_DefinedBenefitPlanAmortizationOfPriorServiceCostCredit"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_DefinedBenefitPlanDisclosureLineItems" xlink:to="locator_us-gaap_DefinedBenefitPlanAmortizationOfPriorServiceCostCredit" use="optional" priority="0" order="2"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DefinedBenefitPlanNetPeriodicBenefitCost" xlink:label="locator_us-gaap_DefinedBenefitPlanNetPeriodicBenefitCost"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_DefinedBenefitPlanDisclosureLineItems" xlink:to="locator_us-gaap_DefinedBenefitPlanNetPeriodicBenefitCost" use="optional" priority="0" order="3"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ScheduleOfDefinedBenefitPlansDisclosuresTable" xlink:label="locator_us-gaap_ScheduleOfDefinedBenefitPlansDisclosuresTable"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="locator_us-gaap_DefinedBenefitPlanDisclosureLineItems" xlink:to="locator_us-gaap_ScheduleOfDefinedBenefitPlansDisclosuresTable" use="optional" priority="0" order="10" xbrldt:contextElement="segment" xbrldt:closed="true"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_RetirementPlanTypeAxis" xlink:label="locator_us-gaap_RetirementPlanTypeAxis"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="locator_us-gaap_ScheduleOfDefinedBenefitPlansDisclosuresTable" xlink:to="locator_us-gaap_RetirementPlanTypeAxis" use="optional" priority="0" order="1"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_RetirementPlanTypeDomain" xlink:label="locator_us-gaap_RetirementPlanTypeDomain"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="locator_us-gaap_RetirementPlanTypeAxis" xlink:to="locator_us-gaap_RetirementPlanTypeDomain" use="optional" priority="0" order="20"/>
    <loc xlink:type="locator" xlink:href="cass-20201231.xsd#cass_SupplementalExecutiveRetirementPlanMember" xlink:label="locator_cass_SupplementalExecutiveRetirementPlanMember"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_RetirementPlanTypeDomain" xlink:to="locator_cass_SupplementalExecutiveRetirementPlanMember" use="optional" priority="0" order="1"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_RetirementPlanTypeDomain" xlink:label="locator_us-gaap_RetirementPlanTypeDomain_a6a67612-0552-334b-30e5-5d5a0128d488_default"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="locator_us-gaap_RetirementPlanTypeAxis" xlink:to="locator_us-gaap_RetirementPlanTypeDomain_a6a67612-0552-334b-30e5-5d5a0128d488_default" use="optional" priority="0" order="30" xbrldt:contextElement="segment"/>
  </definitionLink>
  <definitionLink xlink:type="extended" xlink:role="http://cassinfo.com/role/cass-ebpsotpaiaocld">
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DefinedBenefitPlanDisclosureLineItems" xlink:label="locator_us-gaap_DefinedBenefitPlanDisclosureLineItems"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DefinedBenefitPlanAccumulatedOtherComprehensiveIncomeNetPriorServiceCostCreditBeforeTax" xlink:label="locator_us-gaap_DefinedBenefitPlanAccumulatedOtherComprehensiveIncomeNetPriorServiceCostCreditBeforeTax"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_DefinedBenefitPlanDisclosureLineItems" xlink:to="locator_us-gaap_DefinedBenefitPlanAccumulatedOtherComprehensiveIncomeNetPriorServiceCostCreditBeforeTax" use="optional" priority="0" order="0"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DefinedBenefitPlanAccumulatedOtherComprehensiveIncomeNetGainsLossesBeforeTax" xlink:label="locator_us-gaap_DefinedBenefitPlanAccumulatedOtherComprehensiveIncomeNetGainsLossesBeforeTax"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_DefinedBenefitPlanDisclosureLineItems" xlink:to="locator_us-gaap_DefinedBenefitPlanAccumulatedOtherComprehensiveIncomeNetGainsLossesBeforeTax" use="optional" priority="0" order="1"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DefinedBenefitPlanAccumulatedOtherComprehensiveIncomeBeforeTax" xlink:label="locator_us-gaap_DefinedBenefitPlanAccumulatedOtherComprehensiveIncomeBeforeTax"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_DefinedBenefitPlanDisclosureLineItems" xlink:to="locator_us-gaap_DefinedBenefitPlanAccumulatedOtherComprehensiveIncomeBeforeTax" use="optional" priority="0" order="2"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ScheduleOfDefinedBenefitPlansDisclosuresTable" xlink:label="locator_us-gaap_ScheduleOfDefinedBenefitPlansDisclosuresTable"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="locator_us-gaap_DefinedBenefitPlanDisclosureLineItems" xlink:to="locator_us-gaap_ScheduleOfDefinedBenefitPlansDisclosuresTable" use="optional" priority="0" order="10" xbrldt:contextElement="segment" xbrldt:closed="true"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_RetirementPlanTypeAxis" xlink:label="locator_us-gaap_RetirementPlanTypeAxis"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="locator_us-gaap_ScheduleOfDefinedBenefitPlansDisclosuresTable" xlink:to="locator_us-gaap_RetirementPlanTypeAxis" use="optional" priority="0" order="1"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_RetirementPlanTypeDomain" xlink:label="locator_us-gaap_RetirementPlanTypeDomain"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="locator_us-gaap_RetirementPlanTypeAxis" xlink:to="locator_us-gaap_RetirementPlanTypeDomain" use="optional" priority="0" order="20"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_PensionPlansDefinedBenefitMember" xlink:label="locator_us-gaap_PensionPlansDefinedBenefitMember"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_RetirementPlanTypeDomain" xlink:to="locator_us-gaap_PensionPlansDefinedBenefitMember" use="optional" priority="0" order="1"/>
    <loc xlink:type="locator" xlink:href="cass-20201231.xsd#cass_SupplementalExecutiveRetirementPlanMember" xlink:label="locator_cass_SupplementalExecutiveRetirementPlanMember"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_RetirementPlanTypeDomain" xlink:to="locator_cass_SupplementalExecutiveRetirementPlanMember" use="optional" priority="0" order="11"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_RetirementPlanTypeDomain" xlink:label="locator_us-gaap_RetirementPlanTypeDomain_918f2654-0151-1013-9d17-c88005c4cbdd_default"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="locator_us-gaap_RetirementPlanTypeAxis" xlink:to="locator_us-gaap_RetirementPlanTypeDomain_918f2654-0151-1013-9d17-c88005c4cbdd_default" use="optional" priority="0" order="30" xbrldt:contextElement="segment"/>
  </definitionLink>
  <definitionLink xlink:type="extended" xlink:role="http://cassinfo.com/role/Stock-basedCompensationNarrativeDetails">
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:label="locator_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAuthorized" xlink:label="locator_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAuthorized"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="locator_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAuthorized" use="optional" priority="0" order="0"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod" xlink:label="locator_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="locator_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod" use="optional" priority="0" order="1"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue" xlink:label="locator_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="locator_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue" use="optional" priority="0" order="2"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1" xlink:label="locator_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="locator_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1" use="optional" priority="0" order="3"/>
    <loc xlink:type="locator" xlink:href="cass-20201231.xsd#cass_AmortizationOfRestrictedStockBonus" xlink:label="locator_cass_AmortizationOfRestrictedStockBonus"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="locator_cass_AmortizationOfRestrictedStockBonus" use="optional" priority="0" order="4"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognized" xlink:label="locator_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognized"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="locator_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognized" use="optional" priority="0" order="5"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedPeriodForRecognition1" xlink:label="locator_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedPeriodForRecognition1"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="locator_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedPeriodForRecognition1" use="optional" priority="0" order="6"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsVestedInPeriodFairValue1" xlink:label="locator_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsVestedInPeriodFairValue1"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="locator_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsVestedInPeriodFairValue1" use="optional" priority="0" order="7"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisesInPeriodTotalIntrinsicValue" xlink:label="locator_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisesInPeriodTotalIntrinsicValue"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="locator_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisesInPeriodTotalIntrinsicValue" use="optional" priority="0" order="8"/>
    <loc xlink:type="locator" xlink:href="cass-20201231.xsd#cass_IncentiveStockOptionsExercised" xlink:label="locator_cass_IncentiveStockOptionsExercised"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="locator_cass_IncentiveStockOptionsExercised" use="optional" priority="0" order="9"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable" xlink:label="locator_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="locator_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="locator_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable" use="optional" priority="0" order="10" xbrldt:contextElement="segment" xbrldt:closed="true"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_AwardTypeAxis" xlink:label="locator_us-gaap_AwardTypeAxis"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="locator_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable" xlink:to="locator_us-gaap_AwardTypeAxis" use="optional" priority="0" order="1"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:label="locator_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="locator_us-gaap_AwardTypeAxis" xlink:to="locator_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" use="optional" priority="0" order="20"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_RestrictedStockMember" xlink:label="locator_us-gaap_RestrictedStockMember"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:to="locator_us-gaap_RestrictedStockMember" use="optional" priority="0" order="11"/>
    <loc xlink:type="locator" xlink:href="cass-20201231.xsd#cass_PerformanceBasedRestrictedSharesMember" xlink:label="locator_cass_PerformanceBasedRestrictedSharesMember"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:to="locator_cass_PerformanceBasedRestrictedSharesMember" use="optional" priority="0" order="51"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_StockAppreciationRightsSARSMember" xlink:label="locator_us-gaap_StockAppreciationRightsSARSMember"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:to="locator_us-gaap_StockAppreciationRightsSARSMember" use="optional" priority="0" order="121"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/srt/2020/elts/srt-2020-01-31.xsd#srt_RangeAxis" xlink:label="locator_srt_RangeAxis"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="locator_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable" xlink:to="locator_srt_RangeAxis" use="optional" priority="0" order="2"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/srt/2020/elts/srt-2020-01-31.xsd#srt_RangeMember" xlink:label="locator_srt_RangeMember"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="locator_srt_RangeAxis" xlink:to="locator_srt_RangeMember" use="optional" priority="0" order="20"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/srt/2020/elts/srt-2020-01-31.xsd#srt_MinimumMember" xlink:label="locator_srt_MinimumMember"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_srt_RangeMember" xlink:to="locator_srt_MinimumMember" use="optional" priority="0" order="62"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/srt/2020/elts/srt-2020-01-31.xsd#srt_MaximumMember" xlink:label="locator_srt_MaximumMember"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_srt_RangeMember" xlink:to="locator_srt_MaximumMember" use="optional" priority="0" order="72"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_PlanNameAxis" xlink:label="locator_us-gaap_PlanNameAxis"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="locator_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable" xlink:to="locator_us-gaap_PlanNameAxis" use="optional" priority="0" order="3"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_PlanNameDomain" xlink:label="locator_us-gaap_PlanNameDomain"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="locator_us-gaap_PlanNameAxis" xlink:to="locator_us-gaap_PlanNameDomain" use="optional" priority="0" order="20"/>
    <loc xlink:type="locator" xlink:href="cass-20201231.xsd#cass_PBRSMember" xlink:label="locator_cass_PBRSMember"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_PlanNameDomain" xlink:to="locator_cass_PBRSMember" use="optional" priority="0" order="191"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_StockOptionPlanExpense" xlink:label="locator_us-gaap_StockOptionPlanExpense"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="locator_us-gaap_StockOptionPlanExpense" use="optional" priority="0" order="10"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsOutstandingWeightedAverageRemainingContractualTerms" xlink:label="locator_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsOutstandingWeightedAverageRemainingContractualTerms"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="locator_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsOutstandingWeightedAverageRemainingContractualTerms" use="optional" priority="0" order="11"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingIntrinsicValue" xlink:label="locator_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingIntrinsicValue"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="locator_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingIntrinsicValue" use="optional" priority="0" order="12"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ShareBasedCompensation" xlink:label="locator_us-gaap_ShareBasedCompensation"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="locator_us-gaap_ShareBasedCompensation" use="optional" priority="0" order="13"/>
    <loc xlink:type="locator" xlink:href="cass-20201231.xsd#cass_PercentageOfTargetOpportunityForAwardsToVest" xlink:label="locator_cass_PercentageOfTargetOpportunityForAwardsToVest"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="locator_cass_PercentageOfTargetOpportunityForAwardsToVest" use="optional" priority="0" order="14"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageGrantDateFairValue" xlink:label="locator_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageGrantDateFairValue"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="locator_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageGrantDateFairValue" use="optional" priority="0" order="15"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_PaymentsOfStockIssuanceCosts" xlink:label="locator_us-gaap_PaymentsOfStockIssuanceCosts"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="locator_us-gaap_PaymentsOfStockIssuanceCosts" use="optional" priority="0" order="16"/>
    <loc xlink:type="locator" xlink:href="cass-20201231.xsd#cass_PercentageOfFinancialGoal" xlink:label="locator_cass_PercentageOfFinancialGoal"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="locator_cass_PercentageOfFinancialGoal" use="optional" priority="0" order="17"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardAwardVestingRightsPercentage" xlink:label="locator_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardAwardVestingRightsPercentage"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="locator_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardAwardVestingRightsPercentage" use="optional" priority="0" order="18"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_StockIssuedDuringPeriodSharesNewIssues" xlink:label="locator_us-gaap_StockIssuedDuringPeriodSharesNewIssues"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="locator_us-gaap_StockIssuedDuringPeriodSharesNewIssues" use="optional" priority="0" order="19"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:label="locator_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_519af435-b84a-5c01-5a20-bb24ae6436f7_default"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="locator_us-gaap_AwardTypeAxis" xlink:to="locator_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_519af435-b84a-5c01-5a20-bb24ae6436f7_default" use="optional" priority="0" order="30" xbrldt:contextElement="segment"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/srt/2020/elts/srt-2020-01-31.xsd#srt_RangeMember" xlink:label="locator_srt_RangeMember_2b3806f2-87f6-bd8c-2a03-ee78f6ae4671_default"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="locator_srt_RangeAxis" xlink:to="locator_srt_RangeMember_2b3806f2-87f6-bd8c-2a03-ee78f6ae4671_default" use="optional" priority="0" order="30" xbrldt:contextElement="segment"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_PlanNameDomain" xlink:label="locator_us-gaap_PlanNameDomain_cfca5b04-abf3-409a-38a8-c52d800968f2_default"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="locator_us-gaap_PlanNameAxis" xlink:to="locator_us-gaap_PlanNameDomain_cfca5b04-abf3-409a-38a8-c52d800968f2_default" use="optional" priority="0" order="30" xbrldt:contextElement="segment"/>
  </definitionLink>
  <definitionLink xlink:type="extended" xlink:role="http://cassinfo.com/role/cass-sbcsorsod">
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:label="locator_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsOutstandingRollForward" xlink:label="locator_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsOutstandingRollForward"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="locator_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsOutstandingRollForward" use="optional" priority="0" order="0"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsOutstandingNumber" xlink:label="locator_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsOutstandingNumber"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsOutstandingRollForward" xlink:to="locator_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsOutstandingNumber" use="optional" priority="0" order="1"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod" xlink:label="locator_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsOutstandingRollForward" xlink:to="locator_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod" use="optional" priority="0" order="2"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod" xlink:label="locator_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsOutstandingRollForward" xlink:to="locator_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod" use="optional" priority="0" order="3"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeitedInPeriod" xlink:label="locator_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeitedInPeriod"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsOutstandingRollForward" xlink:to="locator_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeitedInPeriod" use="optional" priority="0" order="4"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward" xlink:label="locator_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="locator_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward" use="optional" priority="0" order="6"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue" xlink:label="locator_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward" xlink:to="locator_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue" use="optional" priority="0" order="7"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageGrantDateFairValue" xlink:label="locator_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageGrantDateFairValue"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward" xlink:to="locator_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageGrantDateFairValue" use="optional" priority="0" order="8"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodWeightedAverageGrantDateFairValue" xlink:label="locator_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodWeightedAverageGrantDateFairValue"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward" xlink:to="locator_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodWeightedAverageGrantDateFairValue" use="optional" priority="0" order="9"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeituresWeightedAverageGrantDateFairValue" xlink:label="locator_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeituresWeightedAverageGrantDateFairValue"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward" xlink:to="locator_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeituresWeightedAverageGrantDateFairValue" use="optional" priority="0" order="10"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable" xlink:label="locator_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="locator_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="locator_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable" use="optional" priority="0" order="10" xbrldt:contextElement="segment" xbrldt:closed="true"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_AwardTypeAxis" xlink:label="locator_us-gaap_AwardTypeAxis"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="locator_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable" xlink:to="locator_us-gaap_AwardTypeAxis" use="optional" priority="0" order="1"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:label="locator_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="locator_us-gaap_AwardTypeAxis" xlink:to="locator_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" use="optional" priority="0" order="20"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_RestrictedStockMember" xlink:label="locator_us-gaap_RestrictedStockMember"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:to="locator_us-gaap_RestrictedStockMember" use="optional" priority="0" order="1"/>
    <loc xlink:type="locator" xlink:href="cass-20201231.xsd#cass_PerformanceBasedRestrictedStockMember" xlink:label="locator_cass_PerformanceBasedRestrictedStockMember"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:to="locator_cass_PerformanceBasedRestrictedStockMember" use="optional" priority="0" order="11"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:label="locator_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_fcd9b13e-f343-ca55-f788-6da67a83e184_default"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="locator_us-gaap_AwardTypeAxis" xlink:to="locator_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_fcd9b13e-f343-ca55-f788-6da67a83e184_default" use="optional" priority="0" order="30" xbrldt:contextElement="segment"/>
  </definitionLink>
  <definitionLink xlink:type="extended" xlink:role="http://cassinfo.com/role/cass-sbcsosod">
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:label="locator_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingRollForward" xlink:label="locator_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingRollForward"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="locator_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingRollForward" use="optional" priority="0" order="0"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber" xlink:label="locator_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingRollForward" xlink:to="locator_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber" use="optional" priority="0" order="1"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriod" xlink:label="locator_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriod"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingRollForward" xlink:to="locator_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriod" use="optional" priority="0" order="2"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised" xlink:label="locator_us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingRollForward" xlink:to="locator_us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised" use="optional" priority="0" order="3"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_StockIssuedDuringPeriodSharesShareBasedCompensationForfeited" xlink:label="locator_us-gaap_StockIssuedDuringPeriodSharesShareBasedCompensationForfeited"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingRollForward" xlink:to="locator_us-gaap_StockIssuedDuringPeriodSharesShareBasedCompensationForfeited" use="optional" priority="0" order="4"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableNumber" xlink:label="locator_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableNumber"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingRollForward" xlink:to="locator_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableNumber" use="optional" priority="0" order="6"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePriceRollforward" xlink:label="locator_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePriceRollforward"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="locator_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePriceRollforward" use="optional" priority="0" order="7"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice" xlink:label="locator_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePriceRollforward" xlink:to="locator_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice" use="optional" priority="0" order="8"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageExercisePrice" xlink:label="locator_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageExercisePrice"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePriceRollforward" xlink:to="locator_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageExercisePrice" use="optional" priority="0" order="9"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsExercisesInPeriodWeightedAverageExercisePrice" xlink:label="locator_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsExercisesInPeriodWeightedAverageExercisePrice"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePriceRollforward" xlink:to="locator_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsExercisesInPeriodWeightedAverageExercisePrice" use="optional" priority="0" order="10"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsForfeituresInPeriodWeightedAverageExercisePrice" xlink:label="locator_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsForfeituresInPeriodWeightedAverageExercisePrice"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePriceRollforward" xlink:to="locator_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsForfeituresInPeriodWeightedAverageExercisePrice" use="optional" priority="0" order="11"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableWeightedAverageExercisePrice" xlink:label="locator_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableWeightedAverageExercisePrice"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePriceRollforward" xlink:to="locator_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableWeightedAverageExercisePrice" use="optional" priority="0" order="13"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable" xlink:label="locator_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="locator_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="locator_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable" use="optional" priority="0" order="10" xbrldt:contextElement="segment" xbrldt:closed="true"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_AwardTypeAxis" xlink:label="locator_us-gaap_AwardTypeAxis"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="locator_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable" xlink:to="locator_us-gaap_AwardTypeAxis" use="optional" priority="0" order="1"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:label="locator_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="locator_us-gaap_AwardTypeAxis" xlink:to="locator_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" use="optional" priority="0" order="20"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_StockAppreciationRightsSARSMember" xlink:label="locator_us-gaap_StockAppreciationRightsSARSMember"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:to="locator_us-gaap_StockAppreciationRightsSARSMember" use="optional" priority="0" order="1"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:label="locator_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_4e75403f-f912-b33f-184f-63f875172e80_default"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="locator_us-gaap_AwardTypeAxis" xlink:to="locator_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_4e75403f-f912-b33f-184f-63f875172e80_default" use="optional" priority="0" order="30" xbrldt:contextElement="segment"/>
  </definitionLink>
  <definitionLink xlink:type="extended" xlink:role="http://cassinfo.com/role/DisclosuresAboutFairValueOfFinancialInstrumentsNarrativeDetails">
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_OtherCommitmentsLineItems" xlink:label="locator_us-gaap_OtherCommitmentsLineItems"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ImpairedFinancingReceivableRelatedAllowance" xlink:label="locator_us-gaap_ImpairedFinancingReceivableRelatedAllowance"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_OtherCommitmentsLineItems" xlink:to="locator_us-gaap_ImpairedFinancingReceivableRelatedAllowance" use="optional" priority="0" order="0"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_OtherCommitmentsTable" xlink:label="locator_us-gaap_OtherCommitmentsTable"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="locator_us-gaap_OtherCommitmentsLineItems" xlink:to="locator_us-gaap_OtherCommitmentsTable" use="optional" priority="0" order="10" xbrldt:contextElement="segment" xbrldt:closed="true"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FinancialInstrumentAxis" xlink:label="locator_us-gaap_FinancialInstrumentAxis"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="locator_us-gaap_OtherCommitmentsTable" xlink:to="locator_us-gaap_FinancialInstrumentAxis" use="optional" priority="0" order="1"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:label="locator_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="locator_us-gaap_FinancialInstrumentAxis" xlink:to="locator_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" use="optional" priority="0" order="20"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_UnfundedLoanCommitmentMember" xlink:label="locator_us-gaap_UnfundedLoanCommitmentMember"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:to="locator_us-gaap_UnfundedLoanCommitmentMember" use="optional" priority="0" order="1"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:label="locator_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_aa7f55e0-09f3-fa7c-b489-086bcf448880_default"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="locator_us-gaap_FinancialInstrumentAxis" xlink:to="locator_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_aa7f55e0-09f3-fa7c-b489-086bcf448880_default" use="optional" priority="0" order="30" xbrldt:contextElement="segment"/>
  </definitionLink>
  <definitionLink xlink:type="extended" xlink:role="http://cassinfo.com/role/DisclosuresAboutFairValueOfFinancialInstrumentsScheduleOfCommitmentsToExtendCreditStandbyLettersOfCreditAndCommercialLettersDetails">
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_OtherCommitmentsLineItems" xlink:label="locator_us-gaap_OtherCommitmentsLineItems"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_LineOfCredit" xlink:label="locator_us-gaap_LineOfCredit"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_OtherCommitmentsLineItems" xlink:to="locator_us-gaap_LineOfCredit" use="optional" priority="0" order="0"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_OtherCommitmentsTable" xlink:label="locator_us-gaap_OtherCommitmentsTable"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="locator_us-gaap_OtherCommitmentsLineItems" xlink:to="locator_us-gaap_OtherCommitmentsTable" use="optional" priority="0" order="10" xbrldt:contextElement="segment" xbrldt:closed="true"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_FinancialInstrumentAxis" xlink:label="locator_us-gaap_FinancialInstrumentAxis"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="locator_us-gaap_OtherCommitmentsTable" xlink:to="locator_us-gaap_FinancialInstrumentAxis" use="optional" priority="0" order="1"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:label="locator_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="locator_us-gaap_FinancialInstrumentAxis" xlink:to="locator_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" use="optional" priority="0" order="20"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_CommitmentsToExtendCreditMember" xlink:label="locator_us-gaap_CommitmentsToExtendCreditMember"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:to="locator_us-gaap_CommitmentsToExtendCreditMember" use="optional" priority="0" order="1"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_CreditFacilityAxis" xlink:label="locator_us-gaap_CreditFacilityAxis"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="locator_us-gaap_OtherCommitmentsTable" xlink:to="locator_us-gaap_CreditFacilityAxis" use="optional" priority="0" order="2"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_CreditFacilityDomain" xlink:label="locator_us-gaap_CreditFacilityDomain"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="locator_us-gaap_CreditFacilityAxis" xlink:to="locator_us-gaap_CreditFacilityDomain" use="optional" priority="0" order="20"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_StandbyLettersOfCreditMember" xlink:label="locator_us-gaap_StandbyLettersOfCreditMember"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_CreditFacilityDomain" xlink:to="locator_us-gaap_StandbyLettersOfCreditMember" use="optional" priority="0" order="11"/>
    <loc xlink:type="locator" xlink:href="cass-20201231.xsd#cass_CommercialLettersOfCreditMember" xlink:label="locator_cass_CommercialLettersOfCreditMember"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_CreditFacilityDomain" xlink:to="locator_cass_CommercialLettersOfCreditMember" use="optional" priority="0" order="21"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:label="locator_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_658fbff9-376a-8135-d6b1-15612e934d22_default"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="locator_us-gaap_FinancialInstrumentAxis" xlink:to="locator_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_658fbff9-376a-8135-d6b1-15612e934d22_default" use="optional" priority="0" order="30" xbrldt:contextElement="segment"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_CreditFacilityDomain" xlink:label="locator_us-gaap_CreditFacilityDomain_63b6cb79-ee6c-b8ba-827b-e0554ac40b5b_default"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="locator_us-gaap_CreditFacilityAxis" xlink:to="locator_us-gaap_CreditFacilityDomain_63b6cb79-ee6c-b8ba-827b-e0554ac40b5b_default" use="optional" priority="0" order="30" xbrldt:contextElement="segment"/>
  </definitionLink>
  <definitionLink xlink:type="extended" xlink:role="http://cassinfo.com/role/cass-isid1">
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_SegmentReportingInformationLineItems" xlink:label="locator_us-gaap_SegmentReportingInformationLineItems"/>
    <loc xlink:type="locator" xlink:href="cass-20201231.xsd#cass_FeeRevenueAndOtherIncomeRevenueFromCustomers" xlink:label="locator_cass_FeeRevenueAndOtherIncomeRevenueFromCustomers"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_SegmentReportingInformationLineItems" xlink:to="locator_cass_FeeRevenueAndOtherIncomeRevenueFromCustomers" use="optional" priority="0" order="0"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_InterestAndOtherIncome" xlink:label="locator_us-gaap_InterestAndOtherIncome"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_SegmentReportingInformationLineItems" xlink:to="locator_us-gaap_InterestAndOtherIncome" use="optional" priority="0" order="1"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_InterestExpense" xlink:label="locator_us-gaap_InterestExpense"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_SegmentReportingInformationLineItems" xlink:to="locator_us-gaap_InterestExpense" use="optional" priority="0" order="2"/>
    <loc xlink:type="locator" xlink:href="cass-20201231.xsd#cass_FeeRevenueAndOtherIncomeIntersegmentIncomeExpense" xlink:label="locator_cass_FeeRevenueAndOtherIncomeIntersegmentIncomeExpense"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_SegmentReportingInformationLineItems" xlink:to="locator_cass_FeeRevenueAndOtherIncomeIntersegmentIncomeExpense" use="optional" priority="0" order="3"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DepreciationAndAmortization" xlink:label="locator_us-gaap_DepreciationAndAmortization"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_SegmentReportingInformationLineItems" xlink:to="locator_us-gaap_DepreciationAndAmortization" use="optional" priority="0" order="4"/>
    <loc xlink:type="locator" xlink:href="cass-20201231.xsd#cass_TaxEquivalizedPretaxIncome" xlink:label="locator_cass_TaxEquivalizedPretaxIncome"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_SegmentReportingInformationLineItems" xlink:to="locator_cass_TaxEquivalizedPretaxIncome" use="optional" priority="0" order="5"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_Goodwill" xlink:label="locator_us-gaap_Goodwill"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_SegmentReportingInformationLineItems" xlink:to="locator_us-gaap_Goodwill" use="optional" priority="0" order="6"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_OtherIntangibleAssetsNet" xlink:label="locator_us-gaap_OtherIntangibleAssetsNet"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_SegmentReportingInformationLineItems" xlink:to="locator_us-gaap_OtherIntangibleAssetsNet" use="optional" priority="0" order="7"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_Assets" xlink:label="locator_us-gaap_Assets"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_SegmentReportingInformationLineItems" xlink:to="locator_us-gaap_Assets" use="optional" priority="0" order="8"/>
    <loc xlink:type="locator" xlink:href="cass-20201231.xsd#cass_FundingSources" xlink:label="locator_cass_FundingSources"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_SegmentReportingInformationLineItems" xlink:to="locator_cass_FundingSources" use="optional" priority="0" order="9"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable" xlink:label="locator_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="locator_us-gaap_SegmentReportingInformationLineItems" xlink:to="locator_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable" use="optional" priority="0" order="10" xbrldt:contextElement="segment" xbrldt:closed="true"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_StatementBusinessSegmentsAxis" xlink:label="locator_us-gaap_StatementBusinessSegmentsAxis"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="locator_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable" xlink:to="locator_us-gaap_StatementBusinessSegmentsAxis" use="optional" priority="0" order="1"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_SegmentDomain" xlink:label="locator_us-gaap_SegmentDomain"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="locator_us-gaap_StatementBusinessSegmentsAxis" xlink:to="locator_us-gaap_SegmentDomain" use="optional" priority="0" order="20"/>
    <loc xlink:type="locator" xlink:href="cass-20201231.xsd#cass_InformationServicesMember" xlink:label="locator_cass_InformationServicesMember"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_SegmentDomain" xlink:to="locator_cass_InformationServicesMember" use="optional" priority="0" order="1"/>
    <loc xlink:type="locator" xlink:href="cass-20201231.xsd#cass_BankingServicesMember" xlink:label="locator_cass_BankingServicesMember"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_SegmentDomain" xlink:to="locator_cass_BankingServicesMember" use="optional" priority="0" order="11"/>
    <loc xlink:type="locator" xlink:href="cass-20201231.xsd#cass_CorporateEliminationsAndOtherMember" xlink:label="locator_cass_CorporateEliminationsAndOtherMember"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_SegmentDomain" xlink:to="locator_cass_CorporateEliminationsAndOtherMember" use="optional" priority="0" order="21"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_SegmentDomain" xlink:label="locator_us-gaap_SegmentDomain_011dfb7a-af0f-8d8f-c0dd-79ae362e7a25_default"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="locator_us-gaap_StatementBusinessSegmentsAxis" xlink:to="locator_us-gaap_SegmentDomain_011dfb7a-af0f-8d8f-c0dd-79ae362e7a25_default" use="optional" priority="0" order="30" xbrldt:contextElement="segment"/>
  </definitionLink>
  <definitionLink xlink:type="extended" xlink:role="http://cassinfo.com/role/LeasesNarrativeDetails">
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_StatementLineItems" xlink:label="locator_us-gaap_StatementLineItems"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_OperatingLeaseLiability" xlink:label="locator_us-gaap_OperatingLeaseLiability"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_StatementLineItems" xlink:to="locator_us-gaap_OperatingLeaseLiability" use="optional" priority="0" order="0"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_OperatingLeaseRightOfUseAsset" xlink:label="locator_us-gaap_OperatingLeaseRightOfUseAsset"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_StatementLineItems" xlink:to="locator_us-gaap_OperatingLeaseRightOfUseAsset" use="optional" priority="0" order="1"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ShortTermLeaseCost" xlink:label="locator_us-gaap_ShortTermLeaseCost"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_StatementLineItems" xlink:to="locator_us-gaap_ShortTermLeaseCost" use="optional" priority="0" order="2"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_OperatingLeaseCost" xlink:label="locator_us-gaap_OperatingLeaseCost"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_StatementLineItems" xlink:to="locator_us-gaap_OperatingLeaseCost" use="optional" priority="0" order="3"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_OperatingLeaseWeightedAverageRemainingLeaseTerm1" xlink:label="locator_us-gaap_OperatingLeaseWeightedAverageRemainingLeaseTerm1"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_StatementLineItems" xlink:to="locator_us-gaap_OperatingLeaseWeightedAverageRemainingLeaseTerm1" use="optional" priority="0" order="4"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_OperatingLeaseWeightedAverageDiscountRatePercent" xlink:label="locator_us-gaap_OperatingLeaseWeightedAverageDiscountRatePercent"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_StatementLineItems" xlink:to="locator_us-gaap_OperatingLeaseWeightedAverageDiscountRatePercent" use="optional" priority="0" order="5"/>
    <loc xlink:type="locator" xlink:href="cass-20201231.xsd#cass_AdditionalOperatingLeaseLiability" xlink:label="locator_cass_AdditionalOperatingLeaseLiability"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_StatementLineItems" xlink:to="locator_cass_AdditionalOperatingLeaseLiability" use="optional" priority="0" order="6"/>
    <loc xlink:type="locator" xlink:href="cass-20201231.xsd#cass_AdditionalOperatingLeaseRightOfUseAsset" xlink:label="locator_cass_AdditionalOperatingLeaseRightOfUseAsset"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_StatementLineItems" xlink:to="locator_cass_AdditionalOperatingLeaseRightOfUseAsset" use="optional" priority="0" order="7"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_OperatingLeasePayments" xlink:label="locator_us-gaap_OperatingLeasePayments"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_StatementLineItems" xlink:to="locator_us-gaap_OperatingLeasePayments" use="optional" priority="0" order="8"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_StatementTable" xlink:label="locator_us-gaap_StatementTable"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="locator_us-gaap_StatementLineItems" xlink:to="locator_us-gaap_StatementTable" use="optional" priority="0" order="10" xbrldt:contextElement="segment" xbrldt:closed="true"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_BalanceSheetLocationAxis" xlink:label="locator_us-gaap_BalanceSheetLocationAxis"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="locator_us-gaap_StatementTable" xlink:to="locator_us-gaap_BalanceSheetLocationAxis" use="optional" priority="0" order="1"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_BalanceSheetLocationDomain" xlink:label="locator_us-gaap_BalanceSheetLocationDomain"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="locator_us-gaap_BalanceSheetLocationAxis" xlink:to="locator_us-gaap_BalanceSheetLocationDomain" use="optional" priority="0" order="20"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_OtherLiabilitiesMember" xlink:label="locator_us-gaap_OtherLiabilitiesMember"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_BalanceSheetLocationDomain" xlink:to="locator_us-gaap_OtherLiabilitiesMember" use="optional" priority="0" order="21"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_OtherAssetsMember" xlink:label="locator_us-gaap_OtherAssetsMember"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_BalanceSheetLocationDomain" xlink:to="locator_us-gaap_OtherAssetsMember" use="optional" priority="0" order="31"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_BalanceSheetLocationDomain" xlink:label="locator_us-gaap_BalanceSheetLocationDomain_453d3386-3e79-ea87-f365-618332cd1d71_default"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="locator_us-gaap_BalanceSheetLocationAxis" xlink:to="locator_us-gaap_BalanceSheetLocationDomain_453d3386-3e79-ea87-f365-618332cd1d71_default" use="optional" priority="0" order="30" xbrldt:contextElement="segment"/>
  </definitionLink>
  <definitionLink xlink:type="extended" xlink:role="http://cassinfo.com/role/LeasesScheduleOfOperatingLeaseLiabilitiesDetails">
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_StatementLineItems" xlink:label="locator_us-gaap_StatementLineItems"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_OperatingLeasesFutureMinimumPaymentsDueAbstract" xlink:label="locator_us-gaap_OperatingLeasesFutureMinimumPaymentsDueAbstract"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_StatementLineItems" xlink:to="locator_us-gaap_OperatingLeasesFutureMinimumPaymentsDueAbstract" use="optional" priority="0" order="0"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_OperatingLeasesFutureMinimumPaymentsDueCurrent" xlink:label="locator_us-gaap_OperatingLeasesFutureMinimumPaymentsDueCurrent"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_OperatingLeasesFutureMinimumPaymentsDueAbstract" xlink:to="locator_us-gaap_OperatingLeasesFutureMinimumPaymentsDueCurrent" use="optional" priority="0" order="1"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_OperatingLeasesFutureMinimumPaymentsDueInTwoYears" xlink:label="locator_us-gaap_OperatingLeasesFutureMinimumPaymentsDueInTwoYears"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_OperatingLeasesFutureMinimumPaymentsDueAbstract" xlink:to="locator_us-gaap_OperatingLeasesFutureMinimumPaymentsDueInTwoYears" use="optional" priority="0" order="2"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_OperatingLeasesFutureMinimumPaymentsDueInThreeYears" xlink:label="locator_us-gaap_OperatingLeasesFutureMinimumPaymentsDueInThreeYears"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_OperatingLeasesFutureMinimumPaymentsDueAbstract" xlink:to="locator_us-gaap_OperatingLeasesFutureMinimumPaymentsDueInThreeYears" use="optional" priority="0" order="3"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_OperatingLeasesFutureMinimumPaymentsDueInFourYears" xlink:label="locator_us-gaap_OperatingLeasesFutureMinimumPaymentsDueInFourYears"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_OperatingLeasesFutureMinimumPaymentsDueAbstract" xlink:to="locator_us-gaap_OperatingLeasesFutureMinimumPaymentsDueInFourYears" use="optional" priority="0" order="4"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_OperatingLeasesFutureMinimumPaymentsDueInFiveYears" xlink:label="locator_us-gaap_OperatingLeasesFutureMinimumPaymentsDueInFiveYears"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_OperatingLeasesFutureMinimumPaymentsDueAbstract" xlink:to="locator_us-gaap_OperatingLeasesFutureMinimumPaymentsDueInFiveYears" use="optional" priority="0" order="5"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_OperatingLeasesFutureMinimumPaymentsDueThereafter" xlink:label="locator_us-gaap_OperatingLeasesFutureMinimumPaymentsDueThereafter"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_OperatingLeasesFutureMinimumPaymentsDueAbstract" xlink:to="locator_us-gaap_OperatingLeasesFutureMinimumPaymentsDueThereafter" use="optional" priority="0" order="6"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_OperatingLeasesFutureMinimumPaymentsDue" xlink:label="locator_us-gaap_OperatingLeasesFutureMinimumPaymentsDue"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_StatementLineItems" xlink:to="locator_us-gaap_OperatingLeasesFutureMinimumPaymentsDue" use="optional" priority="0" order="7"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_LesseeOperatingLeaseLiabilityUndiscountedExcessAmount" xlink:label="locator_us-gaap_LesseeOperatingLeaseLiabilityUndiscountedExcessAmount"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_StatementLineItems" xlink:to="locator_us-gaap_LesseeOperatingLeaseLiabilityUndiscountedExcessAmount" use="optional" priority="0" order="8"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_OperatingLeaseLiability" xlink:label="locator_us-gaap_OperatingLeaseLiability"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_StatementLineItems" xlink:to="locator_us-gaap_OperatingLeaseLiability" use="optional" priority="0" order="9"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_StatementTable" xlink:label="locator_us-gaap_StatementTable"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="locator_us-gaap_StatementLineItems" xlink:to="locator_us-gaap_StatementTable" use="optional" priority="0" order="10" xbrldt:contextElement="segment" xbrldt:closed="true"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_BalanceSheetLocationAxis" xlink:label="locator_us-gaap_BalanceSheetLocationAxis"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="locator_us-gaap_StatementTable" xlink:to="locator_us-gaap_BalanceSheetLocationAxis" use="optional" priority="0" order="1"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_BalanceSheetLocationDomain" xlink:label="locator_us-gaap_BalanceSheetLocationDomain"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="locator_us-gaap_BalanceSheetLocationAxis" xlink:to="locator_us-gaap_BalanceSheetLocationDomain" use="optional" priority="0" order="20"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_OtherLiabilitiesMember" xlink:label="locator_us-gaap_OtherLiabilitiesMember"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_BalanceSheetLocationDomain" xlink:to="locator_us-gaap_OtherLiabilitiesMember" use="optional" priority="0" order="11"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_BalanceSheetLocationDomain" xlink:label="locator_us-gaap_BalanceSheetLocationDomain_2aacfeea-377a-ac63-8dc8-1bcfc694a594_default"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="locator_us-gaap_BalanceSheetLocationAxis" xlink:to="locator_us-gaap_BalanceSheetLocationDomain_2aacfeea-377a-ac63-8dc8-1bcfc694a594_default" use="optional" priority="0" order="30" xbrldt:contextElement="segment"/>
  </definitionLink>
  <definitionLink xlink:type="extended" xlink:role="http://cassinfo.com/role/cass-cfiopcsocbsd">
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/srt/2020/elts/srt-2020-01-31.xsd#srt_CondensedBalanceSheetStatementsCaptionsLineItems" xlink:label="locator_srt_CondensedBalanceSheetStatementsCaptionsLineItems"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_AssetsAbstract" xlink:label="locator_us-gaap_AssetsAbstract"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_srt_CondensedBalanceSheetStatementsCaptionsLineItems" xlink:to="locator_us-gaap_AssetsAbstract" use="optional" priority="0" order="0"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_CashAndDueFromBanks" xlink:label="locator_us-gaap_CashAndDueFromBanks"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_AssetsAbstract" xlink:to="locator_us-gaap_CashAndDueFromBanks" use="optional" priority="0" order="1"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_OtherShortTermInvestments" xlink:label="locator_us-gaap_OtherShortTermInvestments"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_AssetsAbstract" xlink:to="locator_us-gaap_OtherShortTermInvestments" use="optional" priority="0" order="2"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_AvailableForSaleSecurities" xlink:label="locator_us-gaap_AvailableForSaleSecurities"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_AssetsAbstract" xlink:to="locator_us-gaap_AvailableForSaleSecurities" use="optional" priority="0" order="3"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_LoansAndLeasesReceivableNetReportedAmount" xlink:label="locator_us-gaap_LoansAndLeasesReceivableNetReportedAmount"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_AssetsAbstract" xlink:to="locator_us-gaap_LoansAndLeasesReceivableNetReportedAmount" use="optional" priority="0" order="4"/>
    <loc xlink:type="locator" xlink:href="cass-20201231.xsd#cass_PaymentsInExcessOfFunding" xlink:label="locator_cass_PaymentsInExcessOfFunding"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_AssetsAbstract" xlink:to="locator_cass_PaymentsInExcessOfFunding" use="optional" priority="0" order="5"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_InvestmentsInAffiliatesSubsidiariesAssociatesAndJointVentures" xlink:label="locator_us-gaap_InvestmentsInAffiliatesSubsidiariesAssociatesAndJointVentures"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_AssetsAbstract" xlink:to="locator_us-gaap_InvestmentsInAffiliatesSubsidiariesAssociatesAndJointVentures" use="optional" priority="0" order="6"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_PropertyPlantAndEquipmentNet" xlink:label="locator_us-gaap_PropertyPlantAndEquipmentNet"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_AssetsAbstract" xlink:to="locator_us-gaap_PropertyPlantAndEquipmentNet" use="optional" priority="0" order="7"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_OtherAssets" xlink:label="locator_us-gaap_OtherAssets"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_AssetsAbstract" xlink:to="locator_us-gaap_OtherAssets" use="optional" priority="0" order="8"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_Assets" xlink:label="locator_us-gaap_Assets"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_AssetsAbstract" xlink:to="locator_us-gaap_Assets" use="optional" priority="0" order="9"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/srt/2020/elts/srt-2020-01-31.xsd#srt_CondensedBalanceSheetStatementTable" xlink:label="locator_srt_CondensedBalanceSheetStatementTable"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="locator_srt_CondensedBalanceSheetStatementsCaptionsLineItems" xlink:to="locator_srt_CondensedBalanceSheetStatementTable" use="optional" priority="0" order="10" xbrldt:contextElement="segment" xbrldt:closed="true"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_StatementEquityComponentsAxis" xlink:label="locator_us-gaap_StatementEquityComponentsAxis"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="locator_srt_CondensedBalanceSheetStatementTable" xlink:to="locator_us-gaap_StatementEquityComponentsAxis" use="optional" priority="0" order="1"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_EquityComponentDomain" xlink:label="locator_us-gaap_EquityComponentDomain"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="locator_us-gaap_StatementEquityComponentsAxis" xlink:to="locator_us-gaap_EquityComponentDomain" use="optional" priority="0" order="20"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ParentMember" xlink:label="locator_us-gaap_ParentMember"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_EquityComponentDomain" xlink:to="locator_us-gaap_ParentMember" use="optional" priority="0" order="1"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_LiabilitiesAndStockholdersEquityAbstract" xlink:label="locator_us-gaap_LiabilitiesAndStockholdersEquityAbstract"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_srt_CondensedBalanceSheetStatementsCaptionsLineItems" xlink:to="locator_us-gaap_LiabilitiesAndStockholdersEquityAbstract" use="optional" priority="0" order="10"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_LiabilitiesAbstract" xlink:label="locator_us-gaap_LiabilitiesAbstract"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_LiabilitiesAndStockholdersEquityAbstract" xlink:to="locator_us-gaap_LiabilitiesAbstract" use="optional" priority="0" order="11"/>
    <loc xlink:type="locator" xlink:href="cass-20201231.xsd#cass_AccountsAndDraftsPayable" xlink:label="locator_cass_AccountsAndDraftsPayable"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_LiabilitiesAndStockholdersEquityAbstract" xlink:to="locator_cass_AccountsAndDraftsPayable" use="optional" priority="0" order="12"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ShortTermBorrowings" xlink:label="locator_us-gaap_ShortTermBorrowings"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_LiabilitiesAndStockholdersEquityAbstract" xlink:to="locator_us-gaap_ShortTermBorrowings" use="optional" priority="0" order="13"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_OtherLiabilities" xlink:label="locator_us-gaap_OtherLiabilities"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_LiabilitiesAndStockholdersEquityAbstract" xlink:to="locator_us-gaap_OtherLiabilities" use="optional" priority="0" order="14"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_Liabilities" xlink:label="locator_us-gaap_Liabilities"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_LiabilitiesAndStockholdersEquityAbstract" xlink:to="locator_us-gaap_Liabilities" use="optional" priority="0" order="15"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_StockholdersEquity" xlink:label="locator_us-gaap_StockholdersEquity"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_LiabilitiesAndStockholdersEquityAbstract" xlink:to="locator_us-gaap_StockholdersEquity" use="optional" priority="0" order="16"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_LiabilitiesAndStockholdersEquity" xlink:label="locator_us-gaap_LiabilitiesAndStockholdersEquity"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_LiabilitiesAndStockholdersEquityAbstract" xlink:to="locator_us-gaap_LiabilitiesAndStockholdersEquity" use="optional" priority="0" order="17"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_EquityComponentDomain" xlink:label="locator_us-gaap_EquityComponentDomain_659db452-d40c-84ed-955a-64e531cb1932_default"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="locator_us-gaap_StatementEquityComponentsAxis" xlink:to="locator_us-gaap_EquityComponentDomain_659db452-d40c-84ed-955a-64e531cb1932_default" use="optional" priority="0" order="30" xbrldt:contextElement="segment"/>
  </definitionLink>
  <definitionLink xlink:type="extended" xlink:role="http://cassinfo.com/role/cass-cfiopcsocsoid">
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/srt/2020/elts/srt-2020-01-31.xsd#srt_CondensedIncomeStatementsCaptionsLineItems" xlink:label="locator_srt_CondensedIncomeStatementsCaptionsLineItems"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_InvestmentIncomeInterest" xlink:label="locator_us-gaap_InvestmentIncomeInterest"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_srt_CondensedIncomeStatementsCaptionsLineItems" xlink:to="locator_us-gaap_InvestmentIncomeInterest" use="optional" priority="0" order="1"/>
    <loc xlink:type="locator" xlink:href="cass-20201231.xsd#cass_IncomeFromManagementFees" xlink:label="locator_cass_IncomeFromManagementFees"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_srt_CondensedIncomeStatementsCaptionsLineItems" xlink:to="locator_cass_IncomeFromManagementFees" use="optional" priority="0" order="2"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_InvestmentIncomeNonoperating" xlink:label="locator_us-gaap_InvestmentIncomeNonoperating"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_srt_CondensedIncomeStatementsCaptionsLineItems" xlink:to="locator_us-gaap_InvestmentIncomeNonoperating" use="optional" priority="0" order="3"/>
    <loc xlink:type="locator" xlink:href="cass-20201231.xsd#cass_InformationServicesPaymentAndProcessingRevenue" xlink:label="locator_cass_InformationServicesPaymentAndProcessingRevenue"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_srt_CondensedIncomeStatementsCaptionsLineItems" xlink:to="locator_cass_InformationServicesPaymentAndProcessingRevenue" use="optional" priority="0" order="4"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_InterestIncomeExpenseAfterProvisionForLoanLoss" xlink:label="locator_us-gaap_InterestIncomeExpenseAfterProvisionForLoanLoss"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_srt_CondensedIncomeStatementsCaptionsLineItems" xlink:to="locator_us-gaap_InterestIncomeExpenseAfterProvisionForLoanLoss" use="optional" priority="0" order="5"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_DebtAndEquitySecuritiesGainLoss" xlink:label="locator_us-gaap_DebtAndEquitySecuritiesGainLoss"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_srt_CondensedIncomeStatementsCaptionsLineItems" xlink:to="locator_us-gaap_DebtAndEquitySecuritiesGainLoss" use="optional" priority="0" order="6"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_OtherIncome" xlink:label="locator_us-gaap_OtherIncome"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_srt_CondensedIncomeStatementsCaptionsLineItems" xlink:to="locator_us-gaap_OtherIncome" use="optional" priority="0" order="7"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_Revenues" xlink:label="locator_us-gaap_Revenues"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_srt_CondensedIncomeStatementsCaptionsLineItems" xlink:to="locator_us-gaap_Revenues" use="optional" priority="0" order="8"/>
    <loc xlink:type="locator" xlink:href="cass-20201231.xsd#cass_ExpensesAbstract" xlink:label="locator_cass_ExpensesAbstract"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_srt_CondensedIncomeStatementsCaptionsLineItems" xlink:to="locator_cass_ExpensesAbstract" use="optional" priority="0" order="9"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_LaborAndRelatedExpense" xlink:label="locator_us-gaap_LaborAndRelatedExpense"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_cass_ExpensesAbstract" xlink:to="locator_us-gaap_LaborAndRelatedExpense" use="optional" priority="0" order="10"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_OtherExpenses" xlink:label="locator_us-gaap_OtherExpenses"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_cass_ExpensesAbstract" xlink:to="locator_us-gaap_OtherExpenses" use="optional" priority="0" order="11"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/srt/2020/elts/srt-2020-01-31.xsd#srt_CondensedIncomeStatementTable" xlink:label="locator_srt_CondensedIncomeStatementTable"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="locator_srt_CondensedIncomeStatementsCaptionsLineItems" xlink:to="locator_srt_CondensedIncomeStatementTable" use="optional" priority="0" order="10" xbrldt:contextElement="segment" xbrldt:closed="true"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/srt/2020/elts/srt-2020-01-31.xsd#srt_ConsolidatedEntitiesAxis" xlink:label="locator_srt_ConsolidatedEntitiesAxis"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="locator_srt_CondensedIncomeStatementTable" xlink:to="locator_srt_ConsolidatedEntitiesAxis" use="optional" priority="0" order="1"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/srt/2020/elts/srt-2020-01-31.xsd#srt_ConsolidatedEntitiesDomain" xlink:label="locator_srt_ConsolidatedEntitiesDomain"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="locator_srt_ConsolidatedEntitiesAxis" xlink:to="locator_srt_ConsolidatedEntitiesDomain" use="optional" priority="0" order="20"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/srt/2020/elts/srt-2020-01-31.xsd#srt_ParentCompanyMember" xlink:label="locator_srt_ParentCompanyMember"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_srt_ConsolidatedEntitiesDomain" xlink:to="locator_srt_ParentCompanyMember" use="optional" priority="0" order="1"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_NoninterestExpense" xlink:label="locator_us-gaap_NoninterestExpense"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_srt_CondensedIncomeStatementsCaptionsLineItems" xlink:to="locator_us-gaap_NoninterestExpense" use="optional" priority="0" order="12"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest" xlink:label="locator_us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_srt_CondensedIncomeStatementsCaptionsLineItems" xlink:to="locator_us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest" use="optional" priority="0" order="13"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_IncomeTaxExpenseBenefit" xlink:label="locator_us-gaap_IncomeTaxExpenseBenefit"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_srt_CondensedIncomeStatementsCaptionsLineItems" xlink:to="locator_us-gaap_IncomeTaxExpenseBenefit" use="optional" priority="0" order="14"/>
    <loc xlink:type="locator" xlink:href="cass-20201231.xsd#cass_IncomeBeforeUndistributedIncomeOfSubsidiaries" xlink:label="locator_cass_IncomeBeforeUndistributedIncomeOfSubsidiaries"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_srt_CondensedIncomeStatementsCaptionsLineItems" xlink:to="locator_cass_IncomeBeforeUndistributedIncomeOfSubsidiaries" use="optional" priority="0" order="15"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_IncomeLossFromEquityMethodInvestments" xlink:label="locator_us-gaap_IncomeLossFromEquityMethodInvestments"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_srt_CondensedIncomeStatementsCaptionsLineItems" xlink:to="locator_us-gaap_IncomeLossFromEquityMethodInvestments" use="optional" priority="0" order="16"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_NetIncomeLoss" xlink:label="locator_us-gaap_NetIncomeLoss"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_srt_CondensedIncomeStatementsCaptionsLineItems" xlink:to="locator_us-gaap_NetIncomeLoss" use="optional" priority="0" order="17"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/srt/2020/elts/srt-2020-01-31.xsd#srt_ConsolidatedEntitiesDomain" xlink:label="locator_srt_ConsolidatedEntitiesDomain_0fd8506f-b61b-8826-2a0f-9555e9c7a9d2_default"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="locator_srt_ConsolidatedEntitiesAxis" xlink:to="locator_srt_ConsolidatedEntitiesDomain_0fd8506f-b61b-8826-2a0f-9555e9c7a9d2_default" use="optional" priority="0" order="30" xbrldt:contextElement="segment"/>
  </definitionLink>
  <definitionLink xlink:type="extended" xlink:role="http://cassinfo.com/role/cass-cfiopcsosocfd">
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/srt/2020/elts/srt-2020-01-31.xsd#srt_CondensedCashFlowStatementsCaptionsLineItems" xlink:label="locator_srt_CondensedCashFlowStatementsCaptionsLineItems"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_NetCashProvidedByUsedInOperatingActivitiesAbstract" xlink:label="locator_us-gaap_NetCashProvidedByUsedInOperatingActivitiesAbstract"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_srt_CondensedCashFlowStatementsCaptionsLineItems" xlink:to="locator_us-gaap_NetCashProvidedByUsedInOperatingActivitiesAbstract" use="optional" priority="0" order="0"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_NetIncomeLoss" xlink:label="locator_us-gaap_NetIncomeLoss"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_NetCashProvidedByUsedInOperatingActivitiesAbstract" xlink:to="locator_us-gaap_NetIncomeLoss" use="optional" priority="0" order="1"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract" xlink:label="locator_us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_NetCashProvidedByUsedInOperatingActivitiesAbstract" xlink:to="locator_us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract" use="optional" priority="0" order="2"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_IncomeLossFromEquityMethodInvestments" xlink:label="locator_us-gaap_IncomeLossFromEquityMethodInvestments"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract" xlink:to="locator_us-gaap_IncomeLossFromEquityMethodInvestments" use="optional" priority="0" order="3"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_IncreaseDecreaseInOtherOperatingAssets" xlink:label="locator_us-gaap_IncreaseDecreaseInOtherOperatingAssets"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract" xlink:to="locator_us-gaap_IncreaseDecreaseInOtherOperatingAssets" use="optional" priority="0" order="4"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_IncreaseDecreaseInOtherOperatingLiabilities" xlink:label="locator_us-gaap_IncreaseDecreaseInOtherOperatingLiabilities"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract" xlink:to="locator_us-gaap_IncreaseDecreaseInOtherOperatingLiabilities" use="optional" priority="0" order="5"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ShareBasedCompensation" xlink:label="locator_us-gaap_ShareBasedCompensation"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract" xlink:to="locator_us-gaap_ShareBasedCompensation" use="optional" priority="0" order="6"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_AdjustmentForAmortization" xlink:label="locator_us-gaap_AdjustmentForAmortization"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract" xlink:to="locator_us-gaap_AdjustmentForAmortization" use="optional" priority="0" order="7"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_OtherOperatingActivitiesCashFlowStatement" xlink:label="locator_us-gaap_OtherOperatingActivitiesCashFlowStatement"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract" xlink:to="locator_us-gaap_OtherOperatingActivitiesCashFlowStatement" use="optional" priority="0" order="8"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_NetCashProvidedByUsedInOperatingActivities" xlink:label="locator_us-gaap_NetCashProvidedByUsedInOperatingActivities"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_NetCashProvidedByUsedInOperatingActivitiesAbstract" xlink:to="locator_us-gaap_NetCashProvidedByUsedInOperatingActivities" use="optional" priority="0" order="9"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/srt/2020/elts/srt-2020-01-31.xsd#srt_CondensedCashFlowStatementTable" xlink:label="locator_srt_CondensedCashFlowStatementTable"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="locator_srt_CondensedCashFlowStatementsCaptionsLineItems" xlink:to="locator_srt_CondensedCashFlowStatementTable" use="optional" priority="0" order="10" xbrldt:contextElement="segment" xbrldt:closed="true"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/srt/2020/elts/srt-2020-01-31.xsd#srt_ConsolidatedEntitiesAxis" xlink:label="locator_srt_ConsolidatedEntitiesAxis"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="locator_srt_CondensedCashFlowStatementTable" xlink:to="locator_srt_ConsolidatedEntitiesAxis" use="optional" priority="0" order="1"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/srt/2020/elts/srt-2020-01-31.xsd#srt_ConsolidatedEntitiesDomain" xlink:label="locator_srt_ConsolidatedEntitiesDomain"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="locator_srt_ConsolidatedEntitiesAxis" xlink:to="locator_srt_ConsolidatedEntitiesDomain" use="optional" priority="0" order="20"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/srt/2020/elts/srt-2020-01-31.xsd#srt_ParentCompanyMember" xlink:label="locator_srt_ParentCompanyMember"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_srt_ConsolidatedEntitiesDomain" xlink:to="locator_srt_ParentCompanyMember" use="optional" priority="0" order="1"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract" xlink:label="locator_us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_srt_CondensedCashFlowStatementsCaptionsLineItems" xlink:to="locator_us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract" use="optional" priority="0" order="10"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_PaymentsToAcquireAvailableForSaleSecurities" xlink:label="locator_us-gaap_PaymentsToAcquireAvailableForSaleSecurities"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract" xlink:to="locator_us-gaap_PaymentsToAcquireAvailableForSaleSecurities" use="optional" priority="0" order="11"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_PaymentsForProceedsFromLoansAndLeases" xlink:label="locator_us-gaap_PaymentsForProceedsFromLoansAndLeases"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract" xlink:to="locator_us-gaap_PaymentsForProceedsFromLoansAndLeases" use="optional" priority="0" order="12"/>
    <loc xlink:type="locator" xlink:href="cass-20201231.xsd#cass_IncreaseDecreaseInPaymentsInExcessOfFunding" xlink:label="locator_cass_IncreaseDecreaseInPaymentsInExcessOfFunding"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract" xlink:to="locator_cass_IncreaseDecreaseInPaymentsInExcessOfFunding" use="optional" priority="0" order="13"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_PaymentsToAcquirePropertyPlantAndEquipment" xlink:label="locator_us-gaap_PaymentsToAcquirePropertyPlantAndEquipment"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract" xlink:to="locator_us-gaap_PaymentsToAcquirePropertyPlantAndEquipment" use="optional" priority="0" order="14"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_PaymentsToAcquireBusinessesGross" xlink:label="locator_us-gaap_PaymentsToAcquireBusinessesGross"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract" xlink:to="locator_us-gaap_PaymentsToAcquireBusinessesGross" use="optional" priority="0" order="15"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_NetCashProvidedByUsedInInvestingActivities" xlink:label="locator_us-gaap_NetCashProvidedByUsedInInvestingActivities"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract" xlink:to="locator_us-gaap_NetCashProvidedByUsedInInvestingActivities" use="optional" priority="0" order="16"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract" xlink:label="locator_us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_srt_CondensedCashFlowStatementsCaptionsLineItems" xlink:to="locator_us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract" use="optional" priority="0" order="17"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_IncreaseDecreaseInAccountsPayableAndOtherOperatingLiabilities" xlink:label="locator_us-gaap_IncreaseDecreaseInAccountsPayableAndOtherOperatingLiabilities"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract" xlink:to="locator_us-gaap_IncreaseDecreaseInAccountsPayableAndOtherOperatingLiabilities" use="optional" priority="0" order="18"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ProceedsFromShortTermDebt" xlink:label="locator_us-gaap_ProceedsFromShortTermDebt"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract" xlink:to="locator_us-gaap_ProceedsFromShortTermDebt" use="optional" priority="0" order="19"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_PaymentsOfDividendsCommonStock" xlink:label="locator_us-gaap_PaymentsOfDividendsCommonStock"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract" xlink:to="locator_us-gaap_PaymentsOfDividendsCommonStock" use="optional" priority="0" order="20"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_PaymentsForRepurchaseOfCommonStock" xlink:label="locator_us-gaap_PaymentsForRepurchaseOfCommonStock"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract" xlink:to="locator_us-gaap_PaymentsForRepurchaseOfCommonStock" use="optional" priority="0" order="21"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_ProceedsFromPaymentsForOtherFinancingActivities" xlink:label="locator_us-gaap_ProceedsFromPaymentsForOtherFinancingActivities"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract" xlink:to="locator_us-gaap_ProceedsFromPaymentsForOtherFinancingActivities" use="optional" priority="0" order="22"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_NetCashProvidedByUsedInFinancingActivities" xlink:label="locator_us-gaap_NetCashProvidedByUsedInFinancingActivities"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract" xlink:to="locator_us-gaap_NetCashProvidedByUsedInFinancingActivities" use="optional" priority="0" order="23"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsPeriodIncreaseDecreaseExcludingExchangeRateEffect" xlink:label="locator_us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsPeriodIncreaseDecreaseExcludingExchangeRateEffect"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_srt_CondensedCashFlowStatementsCaptionsLineItems" xlink:to="locator_us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsPeriodIncreaseDecreaseExcludingExchangeRateEffect" use="optional" priority="0" order="24"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2020/elts/us-gaap-2020-01-31.xsd#us-gaap_CashAndCashEquivalentsAtCarryingValue" xlink:label="locator_us-gaap_CashAndCashEquivalentsAtCarryingValue"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="locator_srt_CondensedCashFlowStatementsCaptionsLineItems" xlink:to="locator_us-gaap_CashAndCashEquivalentsAtCarryingValue" use="optional" priority="0" order="25"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/srt/2020/elts/srt-2020-01-31.xsd#srt_ConsolidatedEntitiesDomain" xlink:label="locator_srt_ConsolidatedEntitiesDomain_76af1023-df77-eab6-8bbc-413f1eaa6a49_default"/>
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="locator_srt_ConsolidatedEntitiesAxis" xlink:to="locator_srt_ConsolidatedEntitiesDomain_76af1023-df77-eab6-8bbc-413f1eaa6a49_default" use="optional" priority="0" order="30" xbrldt:contextElement="segment"/>
  </definitionLink>
</linkbase>
