    <SEC-DOCUMENT>0001140361-21-036577-index.html : 20211104
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    <ACCEPTANCE-DATETIME>20211104165310
    ACCESSION NUMBER:		0001140361-21-036577
    CONFORMED SUBMISSION TYPE:	S-4
    PUBLIC DOCUMENT COUNT:		22
    FILED AS OF DATE:		20211104
    DATE AS OF CHANGE:		20211104

    FILER:

    	COMPANY DATA:
    		COMPANY CONFORMED NAME:			FIRST INTERSTATE BANCSYSTEM INC
    		CENTRAL INDEX KEY:			0000860413
    		STANDARD INDUSTRIAL CLASSIFICATION:	STATE COMMERCIAL BANKS [6022]
    		IRS NUMBER:				810331430
    		STATE OF INCORPORATION:			MT
    		FISCAL YEAR END:			1231

    	FILING VALUES:
    		FORM TYPE:		S-4
    		SEC ACT:		1933 Act
    		SEC FILE NUMBER:	333-260771
    		FILM NUMBER:		211380820

    	BUSINESS ADDRESS:
    		STREET 1:		P O BOX 30918
    		STREET 2:		401 NO 31ST STREET
    		CITY:			BILLINGS
    		STATE:			MT
    		ZIP:			59116-0918
    		BUSINESS PHONE:		4062555300

    	MAIL ADDRESS:
    		STREET 1:		P O BOX 30918
    		STREET 2:		401 NO 31ST STREET
    		CITY:			BILLINGS
    		STATE:			MT
    		ZIP:			59116-0918

    	FORMER COMPANY:
    		FORMER CONFORMED NAME:	FIRST INTERSTATE BANCSYSTEM OF MONTANA INC
    		DATE OF NAME CHANGE:	19930615
    </SEC-HEADER>
    <DOCUMENT>
    <TYPE>S-4
    <SEQUENCE>1
    <FILENAME>ny20001148x1_s4.htm
    <DESCRIPTION>S-4
    <TEXT>
    Document 1 - file: ny20001148x1_s4.htm

    </DOCUMENT>
    <DOCUMENT>
    <TYPE>EX-23.1
    <SEQUENCE>2
    <FILENAME>ny20001148x1_ex23-1.htm
    <DESCRIPTION>EXHIBIT 23.1
    <TEXT>
    Document 2 - file: ny20001148x1_ex23-1.htm

    </DOCUMENT>
    <DOCUMENT>
    <TYPE>EX-23.2
    <SEQUENCE>3
    <FILENAME>ny20001148x1_ex23-2.htm
    <DESCRIPTION>EXHIBIT 23.2
    <TEXT>
    Document 3 - file: ny20001148x1_ex23-2.htm

    </DOCUMENT>
    <DOCUMENT>
    <TYPE>EX-99.3
    <SEQUENCE>4
    <FILENAME>ny20001148x1_ex99-3.htm
    <DESCRIPTION>EXHIBIT 99.3
    <TEXT>
    Document 4 - file: ny20001148x1_ex99-3.htm

    </DOCUMENT>
    <DOCUMENT>
    <TYPE>EX-99.4
    <SEQUENCE>5
    <FILENAME>ny20001148x1_ex99-4.htm
    <DESCRIPTION>EXHIBIT 99.4
    <TEXT>
    Document 5 - file: ny20001148x1_ex99-4.htm

    </DOCUMENT>
    <DOCUMENT>
    <TYPE>EX-99.5
    <SEQUENCE>6
    <FILENAME>ny20001148x1_ex99-5.htm
    <DESCRIPTION>EXHIBIT 99.5
    <TEXT>
    Document 6 - file: ny20001148x1_ex99-5.htm

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    <SEQUENCE>7
    <FILENAME>header_pipersandler2.jpg
    <TEXT>
    Document 7 - file: header_pipersandler2.jpg

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    <FILENAME>logo_barclays.jpg
    <TEXT>
    Document 8 - file: logo_barclays.jpg

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    <SEQUENCE>9
    <FILENAME>logo_firstinterstatebanx2.jpg
    <TEXT>
    Document 9 - file: logo_firstinterstatebanx2.jpg

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    <FILENAME>logo_firstinterstatebanx3.jpg
    <TEXT>
    Document 10 - file: logo_firstinterstatebanx3.jpg

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    <FILENAME>logo_greatwesternbank.jpg
    <TEXT>
    Document 11 - file: logo_greatwesternbank.jpg

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    <SEQUENCE>12
    <FILENAME>logo_greatwesternbankx1.jpg
    <TEXT>
    Document 12 - file: logo_greatwesternbankx1.jpg

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    <SEQUENCE>13
    <FILENAME>logo_keefe-bruyettewoods.jpg
    <TEXT>
    Document 13 - file: logo_keefe-bruyettewoods.jpg

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    <DOCUMENT>
    <TYPE>GRAPHIC
    <SEQUENCE>14
    <FILENAME>ny20001148x1_ex99-3img01.jpg
    <TEXT>
    Document 14 - file: ny20001148x1_ex99-3img01.jpg

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    <SEQUENCE>15
    <FILENAME>ny20001148x1_ex99-5img01.jpg
    <TEXT>
    Document 15 - file: ny20001148x1_ex99-5img01.jpg

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    <FILENAME>sig_jamesbrannen.jpg
    <TEXT>
    Document 16 - file: sig_jamesbrannen.jpg

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    <SEQUENCE>17
    <FILENAME>sig_keefe-bruyettewoods.jpg
    <TEXT>
    Document 17 - file: sig_keefe-bruyettewoods.jpg

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    <SEQUENCE>18
    <FILENAME>sig_kevinriley.jpg
    <TEXT>
    Document 18 - file: sig_kevinriley.jpg

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    <SEQUENCE>19
    <FILENAME>sig_kevinrileyx1.jpg
    <TEXT>
    Document 19 - file: sig_kevinrileyx1.jpg

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    <FILENAME>sig_markborrecco.jpg
    <TEXT>
    Document 20 - file: sig_markborrecco.jpg

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    <TYPE>GRAPHIC
    <SEQUENCE>21
    <FILENAME>sig_markborreccox1.jpg
    <TEXT>
    Document 21 - file: sig_markborreccox1.jpg

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    <DOCUMENT>
    <TYPE>GRAPHIC
    <SEQUENCE>22
    <FILENAME>sig_pipersandler2.jpg
    <TEXT>
    Document 22 - file: sig_pipersandler2.jpg

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