FIRST INTERSTATE BANCSYSTEM INC — Major Shareholding Notification 2012

Feb 14, 2012

UNITED STATES SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

SCHEDULE 13G

Under the Securities Exchange Act of 1934

(Amendment No. 01 )*

First Interstate BancSystem, Inc

(Name of Issuer)

Common Stock

(Title of Class of Securities)

32055Y201

(CUSIP Number)

December 31, 2011

(Date of Event Which Requires Filing of this Statement)

Check the appropriate box to designate the rule pursuant to which this Schedule is filed:

x Rule 13d-1(b)

o Rule 13d-1(c)

o Rule 13d-1(d)

• The remainder of this cover page shall be filled out for a reporting person’s initial filing on this form with respect to the subject class of securities, and for any subsequent amendment containing information which would alter the disclosures provided in a prior cover page.

The information required in the remainder of this cover page shall not be deemed to be “filed” for the purpose of Section 18 of the Securities Exchange Act of 1934 (“Act”) or otherwise subject to the liabilities of that section of the Act but shall be subject to all other provisions of the Act (however, see the Notes).

CUSIP No. 32055Y201

1	NAMES OF REPORTING PERSONS I.R.S. IDENTIFICATION NOS. OF ABOVE PERSONS (ENTITIES ONLY)
	Legg Mason Capital Management LLC
2	CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP (SEE
INSTRUCTIONS)
	(a) o
	(b) o
3	SEC USE ONLY
4	CITIZENSHIP OR PLACE OF ORGANIZATION
	Maryland
NUMBER OF SHARES
BENEFICIALLY OWNED BY EACH REPORTING PERSON WITH:	5	SOLE VOTING POWER
		0
	6	SHARED VOTING POWER
		1,198,241
	7	SOLE DISPOSITIVE POWER
		0
	8	SHARED DISPOSITIVE POWER
		1,198,241
9	AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING
PERSON
	1,198,241
10	CHECK IF THE AGGREGATE AMOUNT IN ROW (9) EXCLUDES
CERTAIN SHARES (SEE INSTRUCTIONS)
	o
11	PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (9)
	7.33%
12	TYPE OF REPORTING PERSON (SEE INSTRUCTIONS)
	IA
	FOOTNOTES

CUSIP No. 32055Y201

1	NAMES OF REPORTING PERSONS I.R.S. IDENTIFICATION NOS. OF ABOVE PERSONS (ENTITIES ONLY)
	Legg Mason Capital Management Special Investment Trust, Inc.
2	CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP (SEE
INSTRUCTIONS)
	(a) o
	(b) o
3	SEC USE ONLY
4	CITIZENSHIP OR PLACE OF ORGANIZATION
	Maryland
NUMBER OF SHARES
BENEFICIALLY OWNED BY EACH REPORTING PERSON WITH:	5	SOLE VOTING POWER
		0
	6	SHARED VOTING POWER
		942,300
	7	SOLE DISPOSITIVE POWER
		0
	8	SHARED DISPOSITIVE POWER
		942,300
9	AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING
PERSON
	942,300
10	CHECK IF THE AGGREGATE AMOUNT IN ROW (9) EXCLUDES
CERTAIN SHARES (SEE INSTRUCTIONS)
	o
11	PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (9)
	5.77%
12	TYPE OF REPORTING PERSON (SEE INSTRUCTIONS)
	IV
	FOOTNOTES

Item 1.

(a) Name of Issuer

First Interstate Bancsystem, Inc.

(b) Address of Issuer’s Principal Executive Offices

401 North 31st Street Billings, MT 59116

Item 2.

(a) Name of Person Filing

Legg Mason Capital Management LLC Legg Mason Capital Management Special Investment Trust, Inc.

(b) Address of Principal Business Office or, if none, Residence

100 International Drive Baltimore, MD 21202

(c) Citizenship

Maryland Maryland

(d) Title of Class of Securities

Common Stock

(e) CUSIP Number

32055Y201

ITEM 3. If this statement is filed pursuant to §§240.13d-1(b) or 240.13d-2(b) or (c), check whether the person filing is a:

(a) o Broker or dealer registered under section 15 of the Act (15 U.S.C. 78o).

(b) o Bank as defined in section 3(a)(6) of the Act (15 U.S.C. 78c).

(c) o Insurance company as defined in section 3(a)(19) of the Act (15 U.S.C. 78c).

(d) o Investment company registered under section 8 of the Investment Company Act of 1940 (15 U.S.C 80a-8).

(e) x An investment adviser in accordance with §240.13d-1(b)(1)(ii)(E);

(f) o An employee benefit plan or endowment fund in accordance with §240.13d-1(b)(1)(ii)(F);

(g) o A parent holding company or control person in accordance with § 240.13d-1(b)(1)(ii)(G);

(h) o A savings associations as defined in Section 3(b) of the Federal Deposit Insurance Act (12 U.S.C. 1813);

(i) o A church plan that is excluded from the definition of an investment company under section 3(c)(14) of the Investment Company Act of 1940 (15 U.S.C. 80a-3);

(j) o A non-U.S. institution in accordance with § 240.13d-1(b)(1)(ii)(J).

(k) o A group, in accordance with § 240.13d-1(b)(1)(ii)(K). If filing as a non-U.S. institution in accordance with § 240.13d-1(b)(1)(ii)(J), please specify the type of institution:

ITEM 4. Ownership.

Provide the following information regarding the aggregate number and percentage of the class of securities of the issuer identified in Item 1.

(a) Amount beneficially owned: 1,198,241

(b) Percent of class: 7.33

(c) Number of shares as to which the person has:

(i) Sole power to vote or to direct the vote: 0

(ii) Shared power to vote or to direct the vote: 1,198,241

(iii) Sole power to dispose or to direct the disposition of: 0

(iv) Shared power to dispose or to direct the disposition of: 1,198,241

ITEM 5. Ownership of Five Percent or Less of a Class

If this statement is being filed to report the fact that as of the date hereof the reporting person has ceased to be the beneficial owner of more than five percent of the class of securities, check the following o .

N/A

ITEM 6. Ownership of More than Five Percent on Behalf of Another Person.

Various accounts managed by Legg Mason Capital Management have the right to receive or the power to direct the receipt of dividends from, or the proceeds from the sale of shares of the issuer. The interest of Legg Mason Capital Management Special Investment Trust, Inc., an investment company registered under the Investment Company Act of 1940 and managed by Legg Mason Capital Management LLC amounted to 942,300 shares or 5.77% of the total shares outstanding.

ITEM 7. Identification and Classification of the Subsidiary Which Acquired the Security Being Reported on By the Parent Holding Company

N/A

ITEM 8. Identification and Classification of Members of the Group

N/A

ITEM 9. Notice of Dissolution of Group

N/A

| Item
10. |
| --- |
| By signing below I certify that, to the best of my knowledge and belief, the securities referred to above
were acquired and are held in the ordinary course of business and were not acquired and are not held
for the purpose of or with the effect of changing or influencing the control of the issuer of the securities
and were not acquired and are not held in connection with or as a participant in any transaction having
that purpose or effect. |

SIGNATURE

After reasonable inquiry and to the best of my knowledge and belief, I certify that the information set forth in this statement is true, complete and correct.

| /s/
Neil P. O'Callaghan |
| --- |
| Name: Neil P. O'Callaghan |
| Title:
Chief Compliance Officer |

| /s/
Richard M. Wachterman |
| --- |
| Name: Richard M. Wachterman |
| Title:
Assistant Secretary |

Footnotes: This Joint Filing Agreement confirms the agreement by and among the undersigned that the Schedule 13G is filed on behalf of each of the reporting person(s)identified below. Legg Mason Capital Management LLC By: /s/ Neil P. O'Callaghan Neil P. O'Callaghan Chief Compliance Officer Legg Mason Capital Management Special Investment Trust, Inc. By: /s/ Richard M. Wachterman Richard M. Wachterman Assistant Secretary

Attention: Intentional misstatements or omissions of fact constitute Federal criminal violations (See 18 U.S.C. 1001)