<PAGE>

                       SECURITIES AND EXCHANGE COMMISSION
                             WASHINGTON, D.C. 20549

                                    FORM 10-K

                  ANNUAL REPORT PURSUANT TO SECTION 13 OR 15(d)
                     OF THE SECURITIES EXCHANGE ACT OF 1934

For the Fiscal Year Ended                                 Commission file number
   December 31, 2004                                              0-16759

                           FIRST FINANCIAL CORPORATION
             (Exact name of registrant as specified in its charter)

                INDIANA                                   35-1546989
      (State of Incorporation)              (I.R.S. Employer Identification No.)

       One First Financial Plaza
             Terre Haute, IN                               47807
(Address of principal executive offices)                 (Zip Code)

                  Registrant's telephone number: (812) 238-6000

        Securities registered pursuant to Section 12(b) of the Act: None

           Securities registered pursuant to Section 12(g) of the Act:

      TITLE OF EACH CLASS            NAME OF EACH EXCHANGE ON WHICH REGISTERED
   --------------------------        -----------------------------------------
   Common Stock, no par value                         Nasdaq

      Indicated by check mark whether the registrant (1) has filed all reports
required to be filed by Section 13 or 15(d) of the Securities Exchange Act of
1934 during the preceding 12 months, and (2) has been subject to such filing
requirements for the past 90 days. Yes [X]  No [ ]

      Indicate by check mark if disclosure of delinquent filers pursuant to item
405 of regulation S-K is not contained herein, and will not be contained, to the
Registrant's knowledge, in definitive proxy or information statements
incorporated by reference in Part III of the Form 10-K or any amendment to the
form 10-K. [X]

      Indicate by check mark whether the registrant is an accelerated filer (as
defined in Rule 12b-2 of the Act). Yes [X]  No [ ]

      As of June 30, 2004 the aggregate market value of the voting stock held by
nonaffiliates of the registrant based on the average bid and ask prices of such
stock was $393,720,021. (For purposes of this calculation, the Corporation
excluded the stock owned by certain beneficial owners and management and the
Corporation's ESOP.)

      Shares of Common Stock outstanding as of March 9, 2005--13,505,938 shares.

                       DOCUMENTS INCORPORATED BY REFERENCE

      Portions of the 2004 Annual Report to Shareholders are incorporated by
reference into Parts I and II. Portions of the Definitive Proxy Statement for
the First Financial Corporation Annual Meeting of Shareholders to be held April
20, 2005 are incorporated by reference into Part III.

<PAGE>

                         FORM 10-K CROSS-REFERENCE INDEX

<TABLE>
<CAPTION>
                                                                                                              PAGE
<S>                                                                                                           <C>
PART I

    Item 1      Business ..... ............................................................................     2

    Item 2      Properties ................................................................................     2

    Item 3      Legal Proceedings .........................................................................     2

    Item 4      Submission of Matters to a Vote of Security Holders .......................................     2

PART II

    Item 5      Market for Registrant's Common Equity, Related Stockholder Matters
                and Issuer Purchases of Equity Securities .................................................     3

    Item 6      Selected Financial Data ...................................................................     3

    Item 7      Management's Discussion and Analysis of Financial Condition and Results of Operation ......     3

    Item 7 A    Quantitative and Qualitative Disclosures about Market Risk ...............................      3

    Item 8      Financial Statements and Supplementary Data ...............................................     3

    Item 9      Changes in and Disagreements with Accountants on Accounting and Financial Disclosures .....     3

    Item 9 A    Controls and Procedures ...................................................................   3,4

PART III

    Item 10     Directors and Executive Officers of Registrant ............................................     4

    Item 11     Executive Compensation ....................................................................     4

    Item 12     Security Ownership of Certain Beneficial Owners and Management
                and Related Shareholder Matters ...........................................................     4

    Item 13     Certain Relationships and Related Transactions ............................................     4

    Item 14     Principal Accountant Fees and Services ....................................................     4

PART IV

    Item 15     Exhibits and Financial Statement Schedules ................................................     5

                Signatures ................................................................................     6
</TABLE>

                                        1
<PAGE>

                                     PART I

ITEM 1. BUSINESS

      First Financial Corporation (the "Corporation") is a financial services
holding company. The Corporation was originally organized as an Indiana
corporation in 1984 to operate as a bank holding company. For more information
on the Corporation's business, please refer to the following sections of the
2004 Annual Report to Shareholders, which are incorporated by reference into
this Form 10-K:

      1. Description of services, affiliations, number of employees, and
         competition, on pages 30 and 31.

      2. Information regarding supervision of the Corporation, on page 12.

      3. Details regarding competition, on page 30.

ITEM 2. PROPERTIES

      First Financial Corporation is located in a four-story office building in
downtown Terre Haute, Indiana that was first occupied in June 1988. It is leased
to First Financial Bank N.A., a wholly-owned subsidiary (the Bank). The Bank
also owns two other facilities in downtown Terre Haute. One is leased to another
party and the other is a 50,000-square-foot building housing operations and
administrative staff and equipment. In addition, the Bank holds in fee six other
branch buildings. One of the branch buildings is a single-story
36,000-square-foot building which is located in a Terre Haute suburban area. Six
other branch bank buildings are leased by the Bank. The expiration dates on five
of the leases are June 30, 2012, May 31, 2011, February 14, 2011, December 31,
2008, and September 1, 2006. The sixth lease is on a month-to-month basis.

      Facilities of the Corporation's banking centers in Clay County include
three offices in Brazil, Indiana and offices in Clay City and Poland, Indiana.
All five buildings are held in fee.

      Facilities of the Corporation's banking centers in Vermillion County
include two offices in Clinton, Indiana and offices in Cayuga and Newport,
Indiana. All four buildings are held in fee.

      Facilities of the Corporation's banking centers in Sullivan County include
offices in Sullivan, Carlisle, Dugger, Farmersburg and Hymera, Indiana. All five
buildings are held in fee.

      Facilities of the Corporation's banking centers in Greene County include
an office in Worthington, Indiana. This building is held in fee.

      Facilities of the Corporation's banking centers in Knox County include
offices in Monroe City and Sandborn, Indiana. Both buildings are held in fee.

      Facilities of the Corporation's banking centers in Parke County include
two offices in Rockville, Indiana and offices in Marshall, Montezuma and
Rosedale, Indiana. All five buildings are held in fee.

      Facilities of the Corporation's subsidiary, First Crawford State Bank,
include its main office in Robinson, Illinois and two branch facilities in
Oblong and Sumner, Illinois. All three buildings are held in fee by First
Crawford.

      The facility of the Corporation's subsidiary, The Morris Plan Company,
includes an office facility in Terre Haute, Indiana. The building is leased by
The Morris Plan Company. The expiration date on the lease is August 31, 2008.

      Facilities of the Corporation's subsidiary, Forrest Sherer, Inc., include
its main office and one satellite office in Terre Haute, Indiana. The buildings
are held in fee by Forrest Sherer, Inc.

      Facilities of the Corporation's subsidiary, First Community Bank, N.A.,
include its main office in Olney, Illinois, and five branch facilities in Olney,
Lawrenceville, Fairfield, Newton and Charleston, Illinois. All of the buildings
are held in fee by First Community Bank, N.A., except the Olney branch, which is
leased. The expiration date on the lease is March 1, 2010.

ITEM 3.LEGAL PROCEEDINGS

      There are no material pending legal proceedings which involve the
Corporation or its subsidiaries, other than ordinary routine litigation
incidental to its business.

ITEM 4. SUBMISSION OF MATTERS TO A VOTE OF SECURITY HOLDERS

      None

                                        2
<PAGE>

                                     PART II

ITEM 5. MARKET FOR REGISTRANT'S COMMON EQUITY, RELATED STOCKHOLDER MATTERS AND
        ISSUER PURCHASES OF EQUITY SECURITIES

      See "Market and Dividend Information" on page 42 of the 2004 Annual
Report. That portion of the Annual Report is incorporated by reference into this
Form 10-K.

ITEM 6. SELECTED FINANCIAL DATA

      See "Five Year Comparison of Selected Financial Data" on page 7 of the
2004 Annual Report to Shareholders. That portion of the Annual Report is
incorporated by reference into this Form 10-K.

ITEM 7. MANAGEMENT'S DISCUSSION AND ANALYSIS OF FINANCIAL CONDITION AND RESULTS
        OF OPERATION

      See "Management's Discussion and Analysis" on pages 30 through 40 of the
2004 Annual Report to Shareholders. That portion of the Annual Report is
incorporated by reference into this Form 10-K.

ITEM 7A. QUANTITATIVE AND QUALITATIVE DISCLOSURES ABOUT MARKET RISK

      See "Interest Rate Risk" section of "Management's Discussion and Analysis"
on pages 39 and 40 of the 2004 Annual Report to Shareholders. That portion of
the Annual Report is incorporated by reference into this Form 10-K.

ITEM 8.  FINANCIAL STATEMENTS AND SUPPLEMENTARY DATA

      See "Consolidated Balance Sheets" on page 8, "Consolidated Statements of
Income" on page 9, "Consolidated Statements of Changes in Shareholders Equity"
on page 10, "Consolidated Statements of Cash Flows" on page 11, and "Notes to
Consolidated Financial Statements" on pages 12-28. "Report of Independent
Registered Public Accounting Firm on Financial Statements" can be found on page
29 of the 2004 Annual Report to Shareholders. Those portions of the Annual
Report are incorporated by reference into this Form 10-K.

Statistical disclosure by the Corporation includes the following information in
the 2004 Annual Report to Shareholders, which is incorporated by reference into
this Form 10-K:

   1. "Volume/Rate Analysis," on page 32.

   2. "Securities," on page 34.

   3. "Loan Portfolio," on page 35.

   4. "Allowance for Loan Losses," on page 36.

   5. "Nonperforming Loans," on pages 37 and 38.

   6. "Deposits," on page 38.

   7. "Consolidated Balance Sheet-Average Balances and Interest Rates," on page
      41.

ITEM 9. CHANGES IN AND DISAGREEMENTS WITH ACCOUNTANTS ON ACCOUNTING AND
        FINANCIAL DISCLOSURE

      None

ITEM 9A. CONTROLS AND PROCEDURES

EVALUATION OF DISCLOSURE CONTROLS AND PROCEDURES

      As of the end of the period covered by this report, we carried out an
evaluation (the "Evaluation"), under the supervision and with the participation
of our President and Chief Executive Officer ("CEO"), who serves as our
principal executive officer, and Chief Financial Officer ("CFO"), who serves as
our principal financial officer, of the effectiveness of our disclosure controls
and procedures ("Disclosure Controls"). Based on the Evaluation, our CEO and CFO
concluded that our Disclosure Controls are effective in alerting them in a
timely way to material information required to be included in our periodic SEC
reports.

                                        3

<PAGE>
CHANGES IN INTERNAL CONTROLS

      There was no change in the Corporation's internal control over financial
reporting that occurred during the Corporation's fourth fiscal quarter of 2004
that has materially affected, or is reasonably likely to materially affect, the
Corporation's internal control over financial reporting.

MANAGEMENT'S REPORT ON INTERNAL CONTROL OVER FINANCIAL REPORTING

      In reliance upon the Order of the Securities and Exchange Commission
issued under Section 36 of the Securities and Exchange Act of 1934 (Release
No. 50754, November 30, 2004), the Corporation has not included in this Report
either (a) the annual report of its management on the internal control over
financial reporting, as required by Item 308(a) of Regulation S-K, or (b) the
related attestation report of a registered public accounting firm, as required
by Item 308(b) of Regulation S-K. The Corporation will file this information by
amending this Report on or before May 2, 2005. As of the date of this Report,
the Corporation had not identified any material weakness in its internal control
over financial reporting, and the Corporation's registered public accounting
firm had not identified any such material weakness and communicated this finding
to the Corporation.

ITEM 9B. OTHER INFORMATION

      On December 21, 2004, the Corporation extended the term of the existing
employment agreement between Mr. Lowery, First Financial Bank and the
Corporation. The term of the employment agreement will now expire on December
31, 2009. The terms and conditions of the employment agreement are incorporated
by reference from Exhibit 10.1 to this Form 10-K.

      On December 21, 2004, the Compensation Committee of the Company set the
2005 annual base salaries of the named executive officers and established the
criteria under the Corporation's 2001 Long Term Incentive Plan. Salaries as
established for the named executive officers and a summary of the Long Term
Incentive Plan are included as Exhibit 10.4 to this Form 10-K.

      The Company also established the compensation to be paid to Directors for
the year 2005. These amounts are set forth on Exhibit 10.3 to this Form 10-K.

      On February 5, 2005, the Company also approved the bonus amounts payable
to the named executive officers for 2004. These amounts were as follows:

<TABLE>
<CAPTION>
  NAME AND PRINCIPAL POSITION     2004 BONUS AWARD   2004 AWARD UNDER THE 2001 LONG-TERM INCENTIVE PLAN (1)
-------------------------------   ----------------   ------------------------------------------------------
<S>                               <C>                <C>
DONALD E. SMITH                       $150,000                               $375,600
President and Chairman of the
Corporation; Chairman of FFB

NORMAN L. LOWERY                      $150,000                               $312,800
Vice Chairman, CEO and Vice
President of the Corporation;
President and CEO of FFB

MICHAEL A. CARTY                      $ 19,000                               $ 74,000
CFO, Secretary and Treasurer
of the Corporation; Senior Vice
President of FFB

RICHARD O. WHITE                      $ 16,000                               $ 73,500
Senior Vice President of FFB

THOMAS S. CLARY                       $ 16,000                               $ 67,900
Senior Vice President of FFB
and COO
</TABLE>

(1)These amounts represent the amount awarded under the 2001 Long-Term Incentive
   Plan. Payment of these amounts will not begin until the earlier of January 1,
   2015, or the January 1 immediately following the year in which the
   participant reaches the age of 65. These payments generally will be
   annuitized over a 180-month period. Interest accrues on these amounts at
   3.50% from January 1, 2010, until payment begins. When payment begins,
   interest will accrue on the unpaid portion at a 7.00% annual rate compounded
   monthly. The plan requires vesting over a five year period. As such Mr.
   Clary, with two full years of vesting, is entitled to receive only 40% of his
   awarded amount at December 31, 2004.

                                    PART III

ITEM 10. DIRECTORS AND EXECUTIVE OFFICERS OF REGISTRANT

      In accordance with the provisions of General Instruction G to Form 10-K,
the information required for disclosure under Item 10 is not set forth herein
because the Corporation intends to file with the Securities and Exchange
Commission a definitive Proxy Statement pursuant to Regulation 14A not later
than 120 days following the end of its 2004 fiscal year, which Proxy Statement
will contain such information. The information required by Item 10 is
incorporated by reference to such Proxy Statement.

ITEM 11. EXECUTIVE COMPENSATION

      In accordance with the provisions of General Instruction G to Form 10-K,
the information required for disclosure under Item 11 is not set forth herein
because the Corporation intends to file with the Securities and Exchange
Commission a definitive Proxy Statement pursuant to Regulation 14A not later
than 120 days following the end of its 2004 fiscal year, which Proxy Statement
will contain such information. The information required by Item 11 is
incorporated by reference to such Proxy Statement.

ITEM 12. SECURITY OWNERSHIP OF CERTAIN BENEFICIAL OWNERS AND MANAGEMENT

      In accordance with the provisions of General Instruction G to Form 10-K,
the information required for disclosure under Item 12 is not set forth herein
because the Corporation intends to file with the Securities and Exchange
Commission a definitive Proxy Statement pursuant to Regulation 14A not later
than 120 days following the end of its 2004 fiscal year, which Proxy Statement
will contain such information. The information required by Item 12 is
incorporated by reference to such Proxy Statement.

ITEM 13. CERTAIN RELATIONSHIPS AND RELATED TRANSACTIONS

      In accordance with the provisions of General Instruction G to Form 10-K,
the information required for disclosure under Item 13 is not set forth herein
because the Corporation intends to file with the Securities and Exchange
Commission a definitive Proxy Statement pursuant to Regulation 14A not later
than 120 days following the end of its 2004 fiscal year, which Proxy Statement
will contain such information. The information required by Item 13 is
incorporated by reference to such Proxy Statement.

ITEM 14. PRINCIPAL ACCOUNTANT FEES AND SERVICES

      In accordance with the provisions of General Instruction G to Form 10-K,
the information required for disclosure under Item 14 is not set forth herein
because the Corporation intends to file with the Securities and Exchange
Commission a definitive Proxy Statement pursuant to Regulation 14A not later
than 120 days following the end of its 2004 fiscal year, which Proxy Statement
will contain such information. The information required by Item 14 is
incorporated by reference to such Proxy Statement.

                                        4
<PAGE>

                                     PART IV

ITEM 15. EXHIBITS AND FINANCIAL STATEMENT SCHEDULES

   (a)(1) The following consolidated financial statements of the Registrant
          and its subsidiaries are included in the 2004 Annual Report to
          Shareholders of First Financial Corporation attached:

          Consolidated Balance Sheets--December 31, 2004 and 2003

          Consolidated Statements of Income--Years ended December 31, 2004,
          2003, and 2002

          Consolidated Statements of Changes in Shareholders' Equity--Years
          ended December 31, 2004, 2003, and 2002

          Consolidated Statements of Cash Flows--Years ended December 31, 2004,
          2003, and 2002

          Notes to Consolidated Financial Statements

     (2)  Schedules to the Consolidated Financial Statements required by Article
          9 of Regulation S-X are not required, inapplicable, or the required
          information has been disclosed elsewhere.

     (3)  Listing of Exhibits:

<TABLE>
<CAPTION>
Exhibit Number                         Description
--------------    -------------------------------------------------------------------
<S>               <C>
   3.1            Amended and Restated Articles of Incorporation of First Financial
                  Corporation, incorporated by reference to Exhibit 3(i) of the
                  Corporation's Form 10-Q filed for the quarter ended September 30,
                  2002

   3.2            Code of By-Laws of First Financial Corporation, incorporated by
                  reference to Exhibit 3(ii) of the Corporation's Form 10-Q filed for
                  the quarter ended September 30, 2002

   10.1           Employment Agreement for Norman L. Lowery, dated January 1,
                  2004, incorporated by reference to Exhibit 10.2 to the Corporation's
                  Form 10-Q filed for the quarter ended March 31, 2004

   10.2           2001 Long-Term Incentive Plan of First Financial Corporation,
                  incorporated by reference to Exhibit 10.3 of the Corporation's Form
                  10-Q filed for the quarter ended September 30, 2002

   10.3           2005 Schedule of Director Compensation

   10.4           2005 Schedule of Named Executive Officer Compensation

   13             Annual Report

   21             Subsidiaries

   31.1           Certification pursuant to Rule 13a-14(a) for Annual Report
                  of Form 10-K by Principal Executive Officer

   31.2           Certification pursuant to Rule 13a-14(a) for Annual Report
                  of Form 10-K by Principal Financial Officer

   32.1           Certification pursuant to 18 U.S.C. Section 1350
                  of Principal Executive Officer

   32.2           Certification pursuant to 18 U.S.C. Section 1350
                  of Principal Financial Officer
</TABLE>

(b) Exhibits--Exhibits to (a)(3) listed above are attached to this report.

(c) Financial Statements Schedules--No schedules are required to be submitted.
    See response to ITEM 15(a)(2).

                                        5
<PAGE>

                                   SIGNATURES

      Pursuant to the requirements of Section 13 or 15(d) of the Securities
Exchange Act of 1934, the registrant has duly caused this report to be signed on
its behalf by the undersigned, thereunto duly authorized.

                                   First Financial Corporation

                                   Michael A. Carty, signed
                                   ---------------------------------------------
                                   Michael A. Carty, Secretary, Treasurer & CFO
                                   (Principal Financial Officer
                                   and Principal Accounting Officer)

                                   Date: March 15, 2005

Pursuant to the requirements of the Securities Exchange Act of 1934, this report
has been signed below by the following persons on behalf of the registrant and
in the capacities and on the dates indicated.

              NAME                                      DATE

Donald E. Smith, signed                            March 15, 2005
-----------------------------------------------
Donald E. Smith, President and Director

Michael A. Carty, signed                           March 15, 2005
-----------------------------------------------
Michael A. Carty, Secretary, Treasurer & CFO
(Principal Financial Officer
and Principal Accounting Officer)

W. Curtis Brighton, signed                         March 15, 2005
-----------------------------------------------
W. Curtis Brighton, Director

B. Guille Cox, Jr., signed                         March 15, 2005
-----------------------------------------------
B. Guille Cox, Jr., Director

Thomas T. Dinkel, signed                           March 15, 2005
-----------------------------------------------
Thomas T. Dinkel, Director

Anton H. George, signed                            March 15, 2005
-----------------------------------------------
Anton H. George, Director

Gregory L. Gibson, signed                          March 15, 2005
-----------------------------------------------
Gregory L. Gibson, Director

Norman L. Lowery, signed                           March 15, 2005
-----------------------------------------------
Norman L. Lowery, Vice Chairman, CEO & Director
(Principal Executive Officer)

William A. Niemeyer, signed                        March 15, 2005
-----------------------------------------------
William A. Niemeyer, Director

Patrick O'Leary, signed                            March 15, 2005
-----------------------------------------------
Patrick O'Leary, Director
                                                   March 15, 2005
-----------------------------------------------
Chapman J. Root II, Director

Virginia L. Smith, signed                          March 15, 2005
-----------------------------------------------
Virginia L. Smith, Director

                                        6