FORM 4 Check this box if no longer subject to Section 16. Form 4 or Form 5 obligations may continue. See Instruction 1(b).

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 STATEMENT OF CHANGES IN BENEFICIAL OWNERSHIP OF SECURITIES Filed pursuant to Section 16(a) of the Securities Exchange Act of 1934, Section 17(a) of the Public Utility Holding Company Act of 1935 or Section 30(h) of the Investment Company Act of 1940

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(Print or Type Responses)

1. Name and Address of Reporting Person * BROWN ARCHIE M JR   2. Issuer Name and Ticker or Trading Symbol FIRST FINANCIAL BANCORP /OH/ [FFBC] 5. Relationship of Reporting Person(s) to Issuer (Check all applicable) __X__ Director _____ 10% Owner __X__ Officer (give title below) _____ Other (specify below) Chief Executive Officer (Last) (First) (Middle) 255 EAST 5TH STREET, SUITE 2900 3. Date of Earliest Transaction (Month/Day/Year) 04/01/2018 (Street) CINCINNATI, OH 45202 4. If Amendment, Date Original Filed(Month/Day/Year) 6. Individual or Joint/Group Filing(Check Applicable Line) _X_ Form filed by One Reporting Person ___ Form filed by More than One Reporting Person (City) (State) (Zip) Table I - Non-Derivative Securities Acquired, Disposed of, or Beneficially Owned

1.Title of Security (Instr. 3) 2. Transaction Date (Month/Day/Year) 2A. Deemed Execution Date, if any (Month/Day/Year) 3. Transaction Code (Instr. 8) 4. Securities Acquired (A) or Disposed of (D) (Instr. 3, 4 and 5) 5. Amount of Securities Beneficially Owned Following Reported Transaction(s) (Instr. 3 and 4) 6. Ownership Form: Direct (D) or Indirect (I) (Instr. 4) 7. Nature of Indirect Beneficial Ownership (Instr. 4) Code V Amount (A) or (D) Price Common Stock 04/01/2018   A   87,259 A (1) 87,259 D   Common Stock 04/01/2018   A   38,962 A (1) 38,962 I By 401k Common Stock 04/02/2018   A   14,811 A $ 0 14,811 I Restricted Common Stock 04/02/2018   A   14,811 A $ 0 14,811 I Restricted-P

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Table II - Derivative Securities Acquired, Disposed of, or Beneficially Owned
(e.g., puts, calls, warrants, options, convertible securities)

1. Title of Derivative Security (Instr. 3)

2. Conversion or Exercise Price of Derivative Security

3. Transaction Date (Month/Day/Year)

3A. Deemed Execution Date, if any (Month/Day/Year)

4. Transaction Code (Instr. 8)

5. Number of Derivative Securities Acquired (A) or Disposed of (D) (Instr. 3, 4, and 5)

6. Date Exercisable and Expiration Date (Month/Day/Year)

7. Title and Amount of Underlying Securities (Instr. 3 and 4)

8. Price of Derivative Security (Instr. 5)

9. Number of Derivative Securities Beneficially Owned Following Reported Transaction(s) (Instr. 4)

10. Ownership Form of Derivative Security: Direct (D) or Indirect (I) (Instr. 4)

11. Nature of Indirect Beneficial Ownership (Instr. 4)

Code

V

(A)

(D)

Date Exercisable

Expiration Date

Title

Amount or Number of Shares

Employee Stock Option (ISO) Right To Buy

$ 11.59

04/01/2018

A

14,273

12/31/2017

02/03/2024

Common Stock

14,273

(2)

14,273

D

Reporting Owners

Reporting Owner Name / Address	Relationships
	Director	10% Owner	Officer	Other
BROWN ARCHIE M JR 255 EAST 5TH STREET, SUITE 2900 CINCINNATI, OH 45202	X		Chief Executive Officer

Signatures

/s/ Billie L. Meents, POA		04/03/2018
**Signature of Reporting Person		Date

Explanation of Responses:

*	If the form is filed by more than one reporting person, see Instruction 4(b)(v).
**	Intentional misstatements or omissions of facts constitute Federal Criminal Violations. See 18 U.S.C. 1001 and 15 U.S.C. 78ff(a).
(1)	Received pursuant to the merger agreement between First Financial Bancorp. ("First Financial") and MainSource Financial Group, Inc. ("MainSource"), dated July 25, 2017 (the "Merger Agreement"), pursuant to which MainSource was merged with and into First Financial on April 1, 2018 (the "Effective Time"). Pursuant to the Merger Agreement, as of the Effective Time, (i) each issued and outstanding share of MainSource's common stock converted into the right to receive 1.3875 shares of First Financial common stock and cash in lieu of fractional shares (the "Merger Consideration"), and (ii) each outstanding restricted share and each outstanding performance share unit fully vested and was cancelled and converted automatically into the right to receive the Merger Consideration in respect of each share of MainSource's common stock underlying such award, less applicable tax withholdings. On the trading day immediately preceding Effective Date, the closing price of MainSource's common stock was $40.65 per share and the closing price of First Financial's common stock was $29.35 per share.
(2)	Received in the Merger in exchange for an employee stock option to acquire 10,287 shares of MainSource common stock for $11.59 per share.

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