ACNB CORP

UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

WASHINGTON, D.C. 20549

SCHEDULE 14A

(Rule 14a-101)

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SCHEDULE 14A INFORMATION

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ACNB Corporation

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March 30, 2026

Dear Fellow Shareholders of ACNB Corporation:

On behalf of the Board of Directors, I am pleased to inform you of our Annual Meeting of Shareholders to be held virtually via live webcast on Tuesday, May 5, 2026, at 1:00 p.m., prevailing time. You will be able to attend the annual meeting by visiting https://www.cstproxy.com/acnb/2026 and following the instructions on the enclosed proxy card. You will not be able to attend the annual meeting in person. Enclosed with the proxy statement is the notice of meeting, proxy card, ACNB Corporation’s 2025 Annual Review, and ACNB Corporation’s 2025 Annual Report on Form 10-K.

The principal business of the meeting is to elect four (4) Class 3 Directors to serve for terms of three (3) years and until their successors are elected and qualified; to conduct a non-binding vote on executive compensation; to approve and adopt an amendment to the Amended and Restated Articles of Incorporation to increase the authorized number of shares; to approve and adopt an amendment to the Amended and Restated Articles of Incorporation to authorize uncertified shares; to approve, adopt and ratify the ACNB Corporation Employee Stock Purchase Plan; to ratify the selection of Crowe LLP as ACNB Corporation’s independent registered public accounting firm; and, to transact any other business that is properly presented at the annual meeting. The notice of meeting and proxy statement accompanying this letter describe the specific business to be acted upon in more detail.

I urge you to vote as soon as possible by completing, signing and returning the enclosed proxy card in the envelope provided or to vote via the internet or telephone. Your prompt vote will save the Corporation expenses involved in further communications. Your vote is important. Voting by written proxy, internet or telephone will ensure your representation at the annual meeting.

Sincerely,

President & Chief Executive Officer

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NASDAQ TRADING SYMBOL: ACNB

acnb.com

NOTICE OF ANNUAL MEETING OF SHAREHOLDERS

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