<TABLE> <S> <C>

<PAGE>
 
<ARTICLE> 9
<LEGEND>
THIS SCHEDULE CONTAINS SUMMARY FINANCIAL INFORMATION EXTRACTED FROM THE
FINANCIAL STATEMENTS OF INLAND NORTHWEST BANCORPORATION, INC. AS OF AND FOR THE
THREE MONTHS ENDED MARCH 31, 1998 AND IS QUALIFIED IN ITS ENTIRETY BY REFERENCE
TO SUCH FINANCIAL STATEMENTS.
</LEGEND>
<MULTIPLIER> 1,000
       
<S>                             <C>
<PERIOD-TYPE>                   3-MOS
<FISCAL-YEAR-END>                          DEC-31-1998
<PERIOD-START>                             JAN-01-1998
<PERIOD-END>                               MAR-31-1998
<CASH>                                           8,745
<INT-BEARING-DEPOSITS>                             320
<FED-FUNDS-SOLD>                                12,337
<TRADING-ASSETS>                                     0
<INVESTMENTS-HELD-FOR-SALE>                     28,435
<INVESTMENTS-CARRYING>                             819
<INVESTMENTS-MARKET>                               832
<LOANS>                                         83,137
<ALLOWANCE>                                      1,163
<TOTAL-ASSETS>                                 137,312
<DEPOSITS>                                     118,376
<SHORT-TERM>                                     7,774
<LIABILITIES-OTHER>                                990
<LONG-TERM>                                        512
<PREFERRED-MANDATORY>                                0
<PREFERRED>                                          0
<COMMON>                                         8,131
<OTHER-SE>                                       1,529
<TOTAL-LIABILITIES-AND-EQUITY>                 137,312
<INTEREST-LOAN>                                  2,040
<INTEREST-INVEST>                                  454
<INTEREST-OTHER>                                   104
<INTEREST-TOTAL>                                 2,597
<INTEREST-DEPOSIT>                               1,005
<INTEREST-EXPENSE>                                  94
<INTEREST-INCOME-NET>                            1,498
<LOAN-LOSSES>                                       90
<SECURITIES-GAINS>                                   0
<EXPENSE-OTHER>                                  1,357
<INCOME-PRETAX>                                    259
<INCOME-PRE-EXTRAORDINARY>                         151
<EXTRAORDINARY>                                      0
<CHANGES>                                            0
<NET-INCOME>                                       151
<EPS-PRIMARY>                                      .28
<EPS-DILUTED>                                      .24
<YIELD-ACTUAL>                                    4.68
<LOANS-NON>                                        646
<LOANS-PAST>                                       149
<LOANS-TROUBLED>                                    32
<LOANS-PROBLEM>                                  2,630
<ALLOWANCE-OPEN>                                 1,085
<CHARGE-OFFS>                                       12
<RECOVERIES>                                         0
<ALLOWANCE-CLOSE>                                1,163
<ALLOWANCE-DOMESTIC>                             1,163
<ALLOWANCE-FOREIGN>                                  0
<ALLOWANCE-UNALLOCATED>                              0
        

</TABLE>