EXHIBIT 10.3

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September 15, 2017

James M. Anderson

Dear Jamie,

As part of the transition to the “Surviving Corporation” that will be created by
the Agreement and Plan of Merger between First Financial Bancorp and MainSource
Financial Group, Inc. (the “Merger Agreement”), we are pleased to conditionally
offer you the full-time position of Chief Financial Officer, of the Surviving
Corporation, reporting to the Chief Executive Officer. This offer will become
effective as of the “Effective Time” of the merger and is specifically
conditioned upon the “Closing of the Merger” as those terms are defined in the
Merger Agreement. Please refer to the final page of this letter for a full list
of conditions applicable to this offer.

Your total rewards package will include a competitive combination of salary and
incentive pay, benefits, opportunities for career development and a great work
environment that we believe makes First Financial Bank unique.

•
Your starting salary will be $ 360,000 (USD) annually. Your salary will cover
any and all hours you may be required to work in any given workweek. The
position is classified as exempt under the terms of the Fair Labor Standards
Act; therefore, it is not eligible for overtime pay.

•
You will be a participant in the Bank’s Short Term Incentive Plan (STIP). Your
annual target will be 50% of your eligible base compensation. The Short Term
Incentive Plan is an annual cash compensation plan that is based on the
financial performance of the company, as determined by the Compensation
Committee of the Board. The STIP payment you will be eligible to receive for
2018, payable in 2019, will be pro-rated to reflect your eligible base
compensation beginning at the Effective Time.

•
You will be eligible for First Financial Bank’s Long-Term Incentive Plan (LTIP).
Awards are made annually and are fully discretionary based on your individual
performance, as well as your contribution relative to your peers. LTIP awards
are typically delivered in shares of First Financial Bank restricted stock,
which vest evenly over a three-year time frame. LTIP awards are subject to final
approval by the CEO and the Board of Directors. You will be eligible to
participate in LTIP beginning in 2018 with a target of 50%.

•
You will be eligible to receive severance and change in control benefits
pursuant to the attached Severance and Change in Control Agreement. Please note
that your signature

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to Severance and Change in Control Agreement is a condition to your offer and a
condition of your employment with the Surviving Corporation.

•
First Financial Bank offers a full array of health, life, disability and
retirement savings benefits

•
Details of benefit plans you are eligible for will be made available as of
Closing of the Merger.

You will be given the opportunity to enrol in benefits of your selection at a
designated time after the Closing of the Merger.

This letter does not constitute or create nor is it intended to constitute or
create a contract between you and First Financial Bank for employment, hours of
work, or the providing of benefits.  In accepting this conditional offer of
employment, you certify your understanding that your employment will be on an
at-will basis. As an at-will employee, you will be free to terminate your
employment with First Financial Bank at any time, with or without cause or
advance notice. Likewise, First Financial Bank will have the right to reassign
you, to change your compensation and benefits, or to terminate your employment
at any time, with or without cause or advance notice.

I look forward to receiving your signed acceptance of this offer on the
following page of this letter by 5:00 pm on Monday, September 18, 2017. Please
scan it and email it to me at marysue.findley@bankatfirst.com.

If you have any questions, please contact me directly at 513-979-5734 (work) or
513-254-1452 (cell) or marysue.findley@bankatfirst.com. I look forward to
welcoming you to the First Financial Bank team.

Sincerely,

Mary Sue Findley
SVP, Chief Talent Officer

CC:     

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ACCEPTANCE OF OFFER AND CONDITIONS

You acknowledge and agree that, pursuant to the Merger Agreement, this offer is
contingent upon the following: (i) the Closing of the Merger; (ii) you
continuing to be employed by MainSource Bank immediately before the Effective
Time of the merger in the same capacity as you were employed as of the date of
the Merger Agreement; (iii) ratification by the Compensation Committee of the
Board of Directors of the Surviving Corporation; and (iv) your signature to the
attached Severance and Change in Control Agreement prior to the Effective Time.

Additionally, you acknowledge and agree that this offer will become effective as
of the Effective Time. You also acknowledge and agree that should the merger
fail to close, so that there is no Effective Time, this offer shall be void,
with no force or effect.

You acknowledge and agree that this conditional offer letter and the Severance
and Change in Control Agreement represent the entire understanding between you
and First Financial that no verbal or written agreements, promises or
representations that are not specifically stated in this conditional offer or
the Severance and Change in Control Agreement, are or will be binding upon First
Financial.

If you are in agreement with the above, please sign below.

Accepted: /s/ James M. Anderson         Date: September 18, 2017
James M. Anderson