SECURITIES AND EXCHANGE COMMISSION
                             Washington, D.C. 20549

                                  SCHEDULE 13G
                    Under the Securities Exchange Act of 1934
                              (Amendment Number 4)

                            Ohio Casualty Corporation
                                (Name of Issuer)

                                  Common Stock
                         (Title of Class of Securities)

                                    677240103
                                 (CUSIP Number)

                                December 31, 2002
             (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)
[ ] Rule 13d-1(c)
[ ] 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 Notes).

                                  SCHEDULE 13G
CUSIP No. 677240103
--------------------------------------------------------------------------------
1.   Names of Reporting Persons I.R.S. Identification Nos. of Above Persons
     (Entities Only) First Financial Bancorp.
     I.R.S. ID No. 31-1042001
--------------------------------------------------------------------------------
2.   Check the Appropriate Box if a Member of a Group
     (a) [  ]
     (b) [  ]
--------------------------------------------------------------------------------
3.   SEC Use Only

--------------------------------------------------------------------------------
4.   Citizenship or Place of Organization
     Ohio
--------------------------------------------------------------------------------
   Number        5.   Sole Voting Power
  of Shares           3,127,871
 Beneficially    ---------------------------------------------------------------
    Owned        6.   Shared Voting Power
  by Each             0
  Reporting      ---------------------------------------------------------------
   Person        7.   Sole Dispositive Power
    with:             1,127,083
                 ---------------------------------------------------------------
                 8.   Shared Dispositive Power
                      1,715,363
--------------------------------------------------------------------------------
9.   Aggregate Amount Beneficially Owned By Each Reporting Person
     3,139,429
--------------------------------------------------------------------------------
10.  Check Box if the Aggregate Amount in Row (9) Excludes Certain Shares [ ]

--------------------------------------------------------------------------------
11.  Percent of Class Represented by Amount in Row (9)   5.23%

--------------------------------------------------------------------------------
12.  Type of Reporting Person
     HC
--------------------------------------------------------------------------------

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                                  SCHEDULE 13G

CUSIP No. 677240103
--------------------------------------------------------------------------------
1.   Names of Reporting Persons I.R.S. Identification Nos. of Above Persons
     (Entities Only) First Financial Bank N.A.
     I.R.S. ID No. 31-0308605
--------------------------------------------------------------------------------
2.   Check the Appropriate Box if a Member of a Group
     (a) [ ]
     (b) [ ]
--------------------------------------------------------------------------------
3.   SEC Use Only

--------------------------------------------------------------------------------
4.   Citizenship or Place of Organization
     U.S.A.
--------------------------------------------------------------------------------
   Number        5.   Sole Voting Power
  of Shares           3,127,731
 Beneficially    ---------------------------------------------------------------
    Owned        6.   Shared Voting Power
  by Each             0
  Reporting      ---------------------------------------------------------------
   Person        7.   Sole Dispositive Power
    with:             1,126,943
                 ---------------------------------------------------------------
                 8.   Shared Dispositive Power
                      1,715,363
--------------------------------------------------------------------------------
9.   Aggregate Amount Beneficially Owned By Each Reporting Person
     3,139,829
--------------------------------------------------------------------------------
10.  Check Box if the Aggregate Amount in Row (9) Excludes Certain Shares [ ]

--------------------------------------------------------------------------------
11.  Percent of Class Represented by Amount in Row (9)   5.23%

--------------------------------------------------------------------------------
12.  Type of Reporting Person
     BK
--------------------------------------------------------------------------------

                                       3

Item 1(a)  Name of Issuer:
           Ohio Casualty Corporation

Item 1(b)  Address of Issuer's Principal Executive Offices:
           9450 Seward Road
           Fairfield, Ohio 45014

Item 2(a)  Name of Person(s) Filing:
           First Financial Bancorp.

Item 2(b)  Address of Principal Business Office:
           300 High Street
           Hamilton, Ohio 45011

Item 2(c)  Citizenship:
           Ohio

Item 2(d)  Title of Class of Securities:
           Common Stock

Item 2(e)  CUSIP Number:
           677240103

Item 3     If this statement is filed pursuant to Sections 240.13d-1(b) or
           240.13d-2(b) or (c), check whether filing person(s) is (are):

(a)  [ ]  Broker or dealer registered under Section 15 of the Act.
(b)  [x]  Bank as defined in Section 3(a)(6) of the Act.
(c)  [ ]  Insurance company as defined in Section 3(a)(19) of the Act.
(d)  [ ]  Investment company registered under Section 8 of the Investment
          Company Act.
(e)  [ ]  Investment adviser registered under Section 203 of the Investment
          Advisers Act of 1940.
(f)  [ ]  Employee benefit plan, pension fund which is subject to
          provisions of Employee Retirement Income Security Act of 1974 or
          endowment fund; see Rule 13d-1(b)(1)(ii)(F).
(g)  [x]  Parent Holding Company in accordance with Rule 13d-1(b)(1)(ii)(G).
(h)  [ ]  Savings associations as defined in Section 3(b) of the Federal Deposit
          Insurance Act
(i)  [ ]  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
(j)  [ ]  Group, in accordance with Rule 13d-1(b)(1)(ii)(J).

                                       4

Item 4       Ownership

(a)   Amount Beneficially Owned: 3,139,429

(b)   Percent of Class: 5.23%

(c)   Number of Shares as to which person has:

      (i)   Sole power to vote or direct the vote: 3,127,871

      (ii)  Shared power to vote or direct the vote: 0

      (iii) Sole power to dispose or to direct the disposition of: 1,127,083

      (iv)  Shared power to dispose or to direct the disposition of: 1,715,363

Item 5      Ownership of Five Percent or Less of a Class
            N/A

Item 6      Ownership of More than Five Percent on Behalf of Another Person
            The securities covered by this Schedule are held in trust, agency or
            custodial capacities by First Financial Bank, N.A. First Financial
            Bank, N.A. does not know of any person who has the right to direct
            the receipt of dividends from, or the proceeds from the sale of,
            more than five percent of such securities.

Item 7      Identification and Classification of the Subsidiary Which Acquired
            the Security Being Reported on by the Parent Holding Company
            First Financial Bancorp. is a parent holding company in accordance
            with Rule 13d-1(b)(1)(ii)(G); First Financial Bank, N.A., its wholly
            owned subsidiary, is a Bank, as defined in Section 3(a)(6) of the
            Act. See Exhibit 1.

Item 8      Identification and Classification of Members of the Group
            N/A

Item 9      Dissolution of Group
            N/A

Item 10     Certification

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

                                       5

                                    SIGNATURE

      After reasonable inquiry and to the best knowledge and belief of the
undersigned, it is hereby certified that the information set forth in this
statement is true, complete and correct.

Date:  January 31, 2003              First Financial Bancorp.


                                     By:      /s/ Stanley N. Pontius
                                         ---------------------------------------
                                           Stanley N. Pontius, President and CEO


                                     First Financial Bank, N.A.


                                     By:      /s/ Mark W. Immelt
                                         ---------------------------------------
                                           Mark W. Immelt, President and CEO


                                       6

                                    EXHIBIT 1


Identification of Subsidiary       Item 3 Classification

First Financial Bancorp.           Parent Holding Company in accordance with
                                   Rule 13d-1(b)(1)(ii)(G)

First Financial Bank, N.A.         Bank as defined in Section 3(a)(6) of the Act

                                       7