<PAGE>   1
                       SECURITIES AND EXCHANGE COMMISSION
                            Washington, D.C.  20549

                                 FORM 10-K/A

                       FOR ANNUAL AND TRANSITION REPORTS
                    PURSUANT TO SECTIONS 13 OR 15(d) OF THE
                      SECURITIES AND EXCHANGE ACT OF 1934

[X]     Annual Report Pursuant to Section 13 or 15(d) of the Securities Exchange
        Act of 1934
        FEE REQUIRED

        For the Fiscal Year Ended December 31, 1997

                                       OR

        Transition Report Pursuant to Section 13 or 15(d) of the Securities
        Exchange Act of 1934
        NO FEE REQUIRED


        For the transition period from ______________ to ____________

                       Commission File Number: 000-21167

                             CHESTER BANCORP, INC.
             (Exact name of registrant as specified in its charter)


         Delaware                                               37-1359570
(State or other jurisdiction of incorporation               (I.R.S. Employer
        or organization)                                Identification Number)

                 1112 State Street, Chester, Illinois 62233
                  (Address of Principal Executive Offices)

                               (618) 826-5038
            (Registrant's telephone number, including area code)

         Securities Registered Pursuant to Section 12(b) of the Act:
                                    None

         Securities Registered Pursuant to Section 12(g) of the Act:
                   Common Stock, par value $.01 per share
                              (Title of Class)

     Indicate 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 twelve months (or for such shorter period that the
Registrant was required to file such reports) and (2) has been subject to such
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 best of Registrant's knowledge, in definitive proxy or information
statements incorporated by reference in Part III of this Form 10-K or any
amendment to this Form 10-K.  [ ]

     The aggregate market value of the voting stock held by non-affiliates of
the Registrant, computed by reference to the last sale price February 1, 1998,
as reported by the Nasdaq National Market, was approximately $25,084,613.

     As of February 1, 1998 there were 2,182,125 shares issued, of which 
1,953,046 shares were outstanding, of the Registrant's Common Stock.

<PAGE>   2
                                    PART IV

Item 14. Exhibits, Financial Statement Schedules, and Reports on Form 8-K.

(a)(1) Financial Statements

The following information appearing in the Company's Annual Report to
Stockholders for the Fiscal Year Ended December 31, 1997 is incorporated by
reference as Exhibit 13 to this Annual Report on Form 10-K.  No other sections
of such Annual Report are incorporated herein by this reference.


Annual Report Sections

Independent Auditors' Report

Chester Bancorp, Inc. and Subsidiaries Consolidated Balance Sheets for the
     Years Ended December 31, 1997, 1996, and 1995.

Chester Bancorp, Inc. and Subsidiaries Consolidated Statements of Income for
     the Years Ended December 31, 1997, 1996, and 1995.

Chester Bancorp, Inc. and Subsidiaries Consolidated Statements of Stockholders'
     Equity for the Years Ended December 31, 1997, 1996, and 1995.

Chester Bancorp, Inc. and Subsidiaries Consolidated Statements of Cash Flows
     for the Years Ended December 31, 1997, 1996, and 1995.

Chester Bancorp, Inc. and Subsidiaries Notes to Consolidated Financial
     Statements December 31, 1997 and 1996.


(a)(2) Financial Statement Schedules.  Not applicable.

(a)(3) Exhibits


<TABLE>
<CAPTION>
                                                                             Reference to Prior
                                                                             Filing or Exhibit
Regulation S-K                                                               Number Attached
Exhibit Number        Document                                               Hereto
--------------        --------                                               ------------------
<S>                   <C>                                                    <C>
2                     Plan of Conversion of Chester Savings Bank, FSB        (1)
3.1                   Certificate of Incorporation of Chester Bancorp, Inc.  (1)
3.2                   Bylaws of Chester Bancorp.                             (1)
10.1                  Employment Agreement with Michael W. Welge*            (1)
10.2                  Employment Agreement with Edward K. Collins*           (1)
10.3                  Stock Option Plan*                                     (1)
10.4                  Management Recognition and Development Plan*           (1)
10.5                  Employee Stock Ownership Plan and Trust Agreement*     (1)
10.6                  Amended and Restated Director Emeritus Plan            (2)
10.7                  First Amendment to Employment Agreement of Michael     (2)
                      W. Welge dated December 31, 1997
10.8                  First Amendment to Employment Agreement of Edward K.   (2)
                      Collins dated December 31, 1997*
13                    Annual Report to Stockholders for Fiscal Year Ended    13
                      December 31, 1997*
21                    Subsidiaries of Chester Bancorp, Inc.                  (1)
27                    Financial Data Schedule                                (2)
99                    Proxy Statement for the 1998 Annual meeting of the     99
                      Stockholders of Chester Bancorp, Inc.
</TABLE>


(1) Filed as exhibits to the Company's Registration Statement on Form S-1 filed
with the SEC on August 12, 1996.  All such previously filed documents are
hereby incorporated by reference in accordance with Item 601 of Regulation S-K.

(2) Filed as exhibits to the Company's Form 10-K filed with the SEC on March
20, 1998.
        
* These agreements are management contracts or compensation plans or
arrangements required to be filed as exhibits to this Form 10-K.



<PAGE>   3


                                   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.

                             Chester Bancorp, Inc.


March 10, 1998          By    /s/ Michael W. Welge
                            ----------------------------------------
                               Michael W. Welge,
                               Chairman of the Board, President,
                               Chief Financial Officer, and Director


     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.


March 10, 1998          By    /s/ Edward K. Collins
                             -------------------------------------
                                Edward K. Collins,
                                Treasurer, Secretary, and Director

March 10, 1998          By    /s/ Allen R. Verseman
                             -------------------------------------
                                 Allen R. Verseman,
                                 Director

March 10, 1998          By    /s/ Carl H. Welge
                            -------------------------------------
                                 Carl H. Welge,
                                 Director

March 10, 1998          By    /s/ Thomas E. Welch, Jr.
                            -------------------------------------
                                 Thomas E. Welch, Jr.
                                 Director

March 10, 1998          By    /s/ John R. Beck, M.D.
                            -------------------------------------
                                 John R. Beck, M.D.
                                 Director

March 10, 1998          By    /s/ James C. McDonald
                            -------------------------------------
                                 James C. McDonald,
                                 Director



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