Ohio Revised Code Title XXIII. Courts Common Pleas § 2305.117

(1) No action upon a legal malpractice claim against an attorney or a law firm or legal professional association shall be commenced more than four years after the occurrence of the act or omission constituting the alleged basis of the legal malpractice claim.

(2) If an action upon a legal malpractice claim against an attorney or a law firm or legal professional association is not commenced within four years after the occurrence of the act or omission constituting the alleged basis of the claim, then, any action upon that claim is barred.

(C)(1) If a person making a legal malpractice claim against an attorney or a law firm or legal professional association, in the exercise of reasonable care and diligence, could not have discovered the injury resulting from the act or omission constituting the alleged basis of the claim within three years after the occurrence of the act or omission, but, in the exercise of reasonable care and diligence, discovers the injury resulting from that act or omission before the expiration of the four-year period specified in division (B)(1) of this section, the person may commence an action upon the claim not later than one year after the person discovers the injury resulting from that act or omission.

(2) A person who commences an action upon a legal malpractice claim under the circumstances described in division (C)(1) of this section has the affirmative burden of proving, by clear and convincing evidence, that the person, with reasonable care and diligence, could not have discovered the injury resulting from the act or omission constituting the alleged basis of the claim within the three-year period described in that division.