Ohio Rev. Code Ann. § 709.21

No error, irregularity, or defect in the proceedings under sections 709.01 to 709.20 of the Revised Code shall render them invalid once annexation has become final and the annexed territory has been recognized as a part of the annexing municipal corporation, taxes levied upon it as such have been paid, and it has been subjected to the authority of the legislative authority of the annexing municipal corporation.