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                <filerCredentials>
                    <cik>0001908962</cik>
                    <ccc>XXXXXXXX</ccc>
                </filerCredentials>
            </filer>
            <liveTestFlag>LIVE</liveTestFlag>



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        <issuerInfo>
            <issuerCik>0000860413</issuerCik>
            <issuerName>FIRST INTERSTATE BANCSYSTEM INC.</issuerName>
            <secFileNumber>001-34653</secFileNumber>
            <issuerAddress>
                <ns2:street1>401 North 31st Street</ns2:street1>
                <ns2:city>Billings</ns2:city>
                <ns2:stateOrCountry>MT</ns2:stateOrCountry>
                <ns2:zipCode>59101</ns2:zipCode>
            </issuerAddress>
            <issuerContactPhone>(406) 255-5311</issuerContactPhone>
            <nameOfPersonForWhoseAccountTheSecuritiesAreToBeSold>JONATHAN R SCOTT TRUST</nameOfPersonForWhoseAccountTheSecuritiesAreToBeSold>
            <relationshipsToIssuer>
                <relationshipToIssuer>Director</relationshipToIssuer>
            </relationshipsToIssuer>
        </issuerInfo>
        <securitiesInformation>
            <securitiesClassTitle>Common</securitiesClassTitle>
            <brokerOrMarketmakerDetails>
                <name>Morgan Stanley Smith Barney LLC Executive Financial Services</name>
                <address>
                    <ns2:street1>1 New York Plaza</ns2:street1>
                    <ns2:street2>38th Floor</ns2:street2>
                    <ns2:city>New York</ns2:city>
                    <ns2:stateOrCountry>NY</ns2:stateOrCountry>
                    <ns2:zipCode>10004</ns2:zipCode>
                </address>
            </brokerOrMarketmakerDetails>
            <noOfUnitsSold>15000</noOfUnitsSold>
            <aggregateMarketValue>373754.62</aggregateMarketValue>
            <noOfUnitsOutstanding>105018309</noOfUnitsOutstanding>
            <approxSaleDate>09/13/2023</approxSaleDate>
            <securitiesExchangeName>NASDAQ</securitiesExchangeName>
        </securitiesInformation>
        <securitiesToBeSold>
            <securitiesClassTitle>Common</securitiesClassTitle>
            <acquiredDate>07/01/1989</acquiredDate>
            <natureOfAcquisitionTransaction>Gift from Affiliate</natureOfAcquisitionTransaction>
            <nameOfPersonfromWhomAcquired>Thomas Scott</nameOfPersonfromWhomAcquired>
            <isGiftTransaction>Y</isGiftTransaction>
            <donarAcquiredDate>02/15/1972</donarAcquiredDate>
            <amountOfSecuritiesAcquired>15000</amountOfSecuritiesAcquired>
            <natureOfPayment>NA</natureOfPayment>
        </securitiesToBeSold>
        <nothingToReportFlagOnSecuritiesSoldInPast3Months>Y</nothingToReportFlagOnSecuritiesSoldInPast3Months>
        <noticeSignature>
            <noticeDate>09/13/2023</noticeDate>
            <planAdoptionDates/>
            <signature>/s/ Jonathan R Scott</signature>
        </noticeSignature>
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144
0001908962
XXXXXXXX
LIVE
0000860413
FIRST INTERSTATE BANCSYSTEM INC.
001-34653
401 North 31st Street
Billings
MT
59101
(406) 255-5311
JONATHAN R SCOTT TRUST
Director
Common
Morgan Stanley Smith Barney LLC Executive Financial Services
1 New York Plaza
38th Floor
New York
NY
10004
15000
373754.62
105018309
09/13/2023
NASDAQ
Common
07/01/1989
Gift from Affiliate
Thomas Scott
Y
02/15/1972
15000
NA
Y
09/13/2023
/s/ Jonathan R Scott