Ohio Rev. Code Ann. § 164.09
(B)
(F) The bond proceedings, including any trust agreement, may contain additional provisions customary or appropriate to the financing or to the obligations or to particular obligations, including but not limited to:
(Q) Unless a judicial action or proceeding challenging the validity of obligations is commenced by personal service on the treasurer of state prior to the initial delivery of an issue of the obligations, the obligations of that issue and the bond proceedings pertaining to that issue are incontestable and those obligations shall be conclusively considered to be and to have been issued, secured, payable, sold, executed, and delivered, and the bond proceedings relating to them taken, in conformity with law if all of the following apply to the obligations: