First Interstate BancSystem (FIBK) 8-K Results of Operations and Financial Condition

Exhibit 99

Third Quarter 2007

Condensed Consolidated Statements of Income

Three Months Ended            Nine Months Ended September 30, September 30, (Unaudited) 2007 200620072006 (In thousands, except per share data)

Total interest            income $ 83,314^{$76,416$242,784$} 214,943

Total interest expense 32,471^28,614 94,619 75,562

Net interest income 50,843^47,802 148,165 139,381

Provision for loan 1,875 losses............^2,029 5,625 6,360

Net interest income after provision for            loan 48,968 losses.........^45,773 142,540 133,021

Noninterest income 25,390^21,776 69,393 61,713

Noninterest expense 44,581^41,698 129,937 119,367,

Income before taxes 29,777^25,851 81,996 75,367

Income taxes 10,528^9,105 28,626 26,350

Net income $19,249^$16,746 $ 53,370 $ 49,017

DATA PER COMMON SHARE:

Diluted EPS $ 2.32 $^2.02 $ 6.39 $ 5.92

Dividends 0.65^0.58 2.32 1.66

Book value 54.44 47.61

Tangible book value 49.83 43.03

Appraised value 86.75 * 77.25 ** * Based on the latest independent appraised minority share valuation as of June 30, 2007, effective for transactions on or after August 13, 2007. **^{Based on the independent appraised minority share valuation as of June 30, 2006, effective for} transaction on or after August 10, 2006.

Selected Ratios

Three Months Ended            Nine Months Ended September 30, September 30, (Unaudited) 2007 2006 2007 2006

PERFORMANCE

Return on avg common 17.95% equity....^18.01% 16.96% 18.05% Return on avg common equity excl market adj of 17.55% securities......^17.24% 16.69% 17.52% Return on avg assets 1.53%^1.39% ....... 1.44% 1.40% Net interest margin, 4.51% FTE............^4.48% 4.47% 4.50% Efficiency ratio 58.48%^59.93% 59.72% 59.36% CREDIT QUALITY (Period End)

Annualized provision for loan 0.22% losses 0.27% to Annualized net charge offs            to 0.06% average 0.08% Allowance for loan losses to loans 1.46% 1.43% Allowance for loan losses to non-accruing loans 176.30% 293.78% Non-accruing loans to total loans 0.83% 049% CAPITAL ADEQUACY & LIQUIDITY

Leverage capital ratio 8.79% 8.14% Avg loans to avg deposits 88.83% 90.45% Condensed Consolidated Balance Sheets September 30, (Unaudited) 2007 2006 (In thousands)

ASSETS

Cash and due from banks $ 160,875 $ 180,513

Federal funds sold 32,961 21,354

Interest bearing deposits 8,419 5,360

Investment securities 992,753 1,051,000

Loans 3,528,108 3,288,470

Less: allowance for loan losses 51,452 46,957

Net loans 3,476,656 3,241,513

Premises & equipment, net 123,425 119,796

Accrued interest receivable 38,733 34,046

Goodwill 37,380 37,380

Mortgage servicing rights 22,399 23,708

Company owned life insurance 66,332 64,071

Other assets 51,674 45,218

Total Assets $5,011,607 $4,823,959

LIABILITIES AND STOCKHOLDERS’ EQUITY

Deposits $4,005,310 $3,616,063

Federal funds purchased 63,830

Securities sold under repurchase agreements 458,787 634,581

Other liabilities 51,484 45,260

Other borrowed funds 8,164 5,941

Long — term debt 5,509 28,564

Subordinated debenture 41,238 41,238

Total Liabilities 4,570,492 4,435,477

Common stockholders’ equity 441,115 388,482

Total Liabilities and Stockholders’ Equity $5,011,607 $4,823,959

Net Interest Margin, FTE

4 .70 4 .6 0 average loans 4 .50 ........

4 .4 0

%

4 .3 0 4 .2 0 4 .10 4 .0 0

3 Q0 5 4 Q0 5 1Q0 6 2 Q0 6 3 Q0 6 4 Q0 6 1Q0 7 2 Q0 7 3 Q0 7

Quarters

First Interstate BancSystem, Inc.

P.O. Box 30918oBillings, Montana 59116o(406) 255-5390 www.firstinterstatebank.com

First InterstateBancSystem, Inc.

Third Quarter 2007

To our shareholders, First Interstate BancSystem is pleased to announce record third quarter 2007 net income of $19,249,000, or $2.32 per diluted share, as compared to $16,746,000, or $2.02 per diluted share, during third quarter 2006. Third quarter 2007 return on average common equity was 17.95% and return on average assets was 1.53%, compared to 18.01% and 1.39%, respectively, during third quarter 2006.

Quarterly Results Third quarter 2007 net interest income of $50,843,000 was $3,857,000 higher than in third quarter 2006, primarily due to organic loan growth. The net interest margin ratio of 4.51% increased 3 basis points from third quarter 2006. Average loans grew $250,967,000, or 8%, during third quarter 2007 as compared to the same period last year and average deposits grew $422,996,000 or 12%. Average repurchase (or Repo) agreements decreased $175,409,000, or 27%, during third quarter 2007, as compared to the same period last year primarily due to the migration of Repo customers to our new money market sweep deposit product introduced during first quarter 2007. The third quarter 2007 provision for loan losses of $1,875,000 was $154,000, or 8%, lower than the third quarter 2006 provision.

Noninterest income of $25,390,000 was $3,614,000, or 17%, higher than third quarter 2006. Third quarter 2007 noninterest income was positively impacted by a nonrecurring technology services contract termination fee of $2,037,000 and a nonre-curring gain from the conversion and subsequent sale of MasterCard stock of $737,000. Other major components of the quarter-over-quarter increase include additional fee income from higher volumes of debit and credit card transactions and increases in revenue from fiduciary activities, which increased $515,000 and $364,000, respectively, from third quarter 2006.

Noninterest expense of $44,581,000 was $2,883,000, or 7%, higher than third quarter 2006. Salary and benefits expense increased $2,224,000, or 10%, primarily due to the combined effects of inflationary wage increases, higher staffing levels, higher incentive and profit sharing accruals and increases in group medical insurance costs. In addition, occupancy expense increased $671,000, or 21%, as compared to third quarter 2006, primarily due to higher depreciation and maintenance expenses. Impairment charges related to mortgage servicing rights decreased $559,000 during third quarter 2007, as compared to the same period in 2006.

On October 5, 2007, we paid dividends of $0.65 per common share.

Year-to-Date Results

Year-to-date net income of $53,370,000, or $6.40 per diluted share, increased 4,353,000, or 9%, from $49,017,000, or $5.92 per diluted share, during the same period in 2006. Return on average equity was 16.96% for the first three quarters of 2007, as compared to 18.05% for the same period in 2006, return on average assets was 1.44% versus 1.40%.

Financial Highlights Three Months ended September 30, (Unaudited) 2007 2006 % Change (In thousands, except per share data)

OPERATING RESULTS

Net income $ 19,249 $ 16,746 14.9% Diluted earnings per share 2.32 2.02 14.7% Dividends per share 0.65 0.58 12.1%

PERIOD END BALANCES

Assets 5,011,607 4,823,959 3.9% Loans 3,528,108 3,288,470 7.3% Investment securities 992,753 1,051,000 -5.5% Deposits 4,005,310 3,616,063 10.8% Common stockholders’ equity 441,115 388,482 13.5% Common shares outstanding 8,102 8,160 -0.7% QUARTERLY AVERAGES

Assets 4,988,835 4,767,599 4.6% Loans 3,523,170 3,272,203 7.7% Investment securities 985,381 1,015,254 -2.9% Deposits 3,981,321 3,558,325 11.9% Common stockholders’ equity 425,476 368,980 15.3% Common shares outstanding 8,109 8,093 0.2%

Although our year-to-date net interest income of $148,165,000 increased $8,784,000, or 6%, from the same period in 2006, our net interest margin ratio declined 3 basis points to 4.47%.

Total assets as of September 30, 2007 exceeded $5 billion. This milestone would not have been possible without the dedication of our talented team of employees, directors and advisory directors. Thank you and hearty congratulations!

In September 2007, we entered into an agreement with First Western Bancorp of South Dakota to acquire its banking and data servicing subsidiaries, with combined assets of approximately $1 billion. The transaction is expected to close during first quarter 2008. This is our first acquisition outside of our home states of Montana and Wyoming. We are excited about this opportunity to expand our market area into western South Dakota and are pleased to have First Western join the First Interstate family.

Lyle R. Knight            Terrill R. Moore

President            Executive Vice President

Chief Executive Officer            Chief Financial Officer