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        <filerInfo>
            <filer>
                <filerCredentials>
                    <cik>0001908851</cik>
                    <ccc>XXXXXXXX</ccc>
                </filerCredentials>
            </filer>
            <liveTestFlag>LIVE</liveTestFlag>



        </filerInfo>
    </headerData>
    <formData>
        <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>JULIE SCOTT ROSE TRUST UAD 12/20/89</nameOfPersonForWhoseAccountTheSecuritiesAreToBeSold>
            <relationshipsToIssuer>
                <relationshipToIssuer>Family Ownership</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>13400</noOfUnitsSold>
            <aggregateMarketValue>312902.84</aggregateMarketValue>
            <noOfUnitsOutstanding>105018309</noOfUnitsOutstanding>
            <approxSaleDate>10/27/2023</approxSaleDate>
            <securitiesExchangeName>NASDAQ</securitiesExchangeName>
        </securitiesInformation>
        <securitiesToBeSold>
            <securitiesClassTitle>Common</securitiesClassTitle>
            <acquiredDate>06/20/2020</acquiredDate>
            <natureOfAcquisitionTransaction>Distribution from a Trust or an Estate</natureOfAcquisitionTransaction>
            <nameOfPersonfromWhomAcquired>Joan Scott</nameOfPersonfromWhomAcquired>
            <isGiftTransaction>N</isGiftTransaction>
            <amountOfSecuritiesAcquired>13400</amountOfSecuritiesAcquired>
            <paymentDate>06/20/2020</paymentDate>
            <natureOfPayment>Not Applicable</natureOfPayment>
        </securitiesToBeSold>
        <nothingToReportFlagOnSecuritiesSoldInPast3Months>N</nothingToReportFlagOnSecuritiesSoldInPast3Months>
        <securitiesSoldInPast3Months>
            <sellerDetails>
                <name>JULIE SCOTT ROSE TRUST UAD 12/20/89</name>
                <address>
                    <ns2:street1>401 North 31st Street</ns2:street1>
                    <ns2:city>Billings</ns2:city>
                    <ns2:stateOrCountry>MT</ns2:stateOrCountry>
                    <ns2:zipCode>59101</ns2:zipCode>
                </address>
            </sellerDetails>
            <securitiesClassTitle>Common</securitiesClassTitle>
            <saleDate>09/13/2023</saleDate>
            <amountOfSecuritiesSold>20000</amountOfSecuritiesSold>
            <grossProceeds>501844.00</grossProceeds>
        </securitiesSoldInPast3Months>
        <securitiesSoldInPast3Months>
            <sellerDetails>
                <name>JULIE SCOTT ROSE TRUST UAD 12/20/89</name>
                <address>
                    <ns2:street1>401 North 31st Street</ns2:street1>
                    <ns2:city>Billings</ns2:city>
                    <ns2:stateOrCountry>MT</ns2:stateOrCountry>
                    <ns2:zipCode>59101</ns2:zipCode>
                </address>
            </sellerDetails>
            <securitiesClassTitle>Common</securitiesClassTitle>
            <saleDate>09/12/2023</saleDate>
            <amountOfSecuritiesSold>11928</amountOfSecuritiesSold>
            <grossProceeds>298654.00</grossProceeds>
        </securitiesSoldInPast3Months>
        <securitiesSoldInPast3Months>
            <sellerDetails>
                <name>JULIE SCOTT ROSE TRUST UAD 12/20/89</name>
                <address>
                    <ns2:street1>401 North 31st Street</ns2:street1>
                    <ns2:city>Billings</ns2:city>
                    <ns2:stateOrCountry>MT</ns2:stateOrCountry>
                    <ns2:zipCode>59101</ns2:zipCode>
                </address>
            </sellerDetails>
            <securitiesClassTitle>Common</securitiesClassTitle>
            <saleDate>09/11/2023</saleDate>
            <amountOfSecuritiesSold>8072</amountOfSecuritiesSold>
            <grossProceeds>201450.00</grossProceeds>
        </securitiesSoldInPast3Months>
        <noticeSignature>
            <noticeDate>10/27/2023</noticeDate>
            <planAdoptionDates/>
            <signature>/s/ Julie Scott Rose</signature>
        </noticeSignature>
    </formData>
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144
0001908851
XXXXXXXX
LIVE
0000860413
FIRST INTERSTATE BANCSYSTEM INC.
001-34653
401 North 31st Street
Billings
MT
59101
(406) 255-5311
JULIE SCOTT ROSE TRUST UAD 12/20/89
Family Ownership
Common
Morgan Stanley Smith Barney LLC Executive Financial Services
1 New York Plaza
38th Floor
New York
NY
10004
13400
312902.84
105018309
10/27/2023
NASDAQ
Common
06/20/2020
Distribution from a Trust or an Estate
Joan Scott
N
13400
06/20/2020
Not Applicable
N
JULIE SCOTT ROSE TRUST UAD 12/20/89
401 North 31st Street
Billings
MT
59101
Common
09/13/2023
20000
501844.00
JULIE SCOTT ROSE TRUST UAD 12/20/89
401 North 31st Street
Billings
MT
59101
Common
09/12/2023
11928
298654.00
JULIE SCOTT ROSE TRUST UAD 12/20/89
401 North 31st Street
Billings
MT
59101
Common
09/11/2023
8072
201450.00
10/27/2023
/s/ Julie Scott Rose