Ohio Rev. Code § 5309.12
The applicant desiring to register the title to land or to any interest therein shall be regarded as plaintiff and all other persons named in the application and to be affected by the decree shall by name be entered in the caption of the petition and treated as defendants, and all persons not so named, whether mentioned in the application or not, shall be included and considered as defendants under the designation, which shall appear in the caption of the petition, "all other persons, if any, having any right or interest in or lien upon the lands, or any part thereof, described herein."
When the names of any persons or heirs or devisees of a deceased person, necessary or proper to be made parties defendant to an application, are unknown to the applicant after diligent inquiry and research, the character and extent of which shall be stated, or if the applicant is unable to ascertain whether a person who is a necessary party is living or dead, or if dead whether he died testate or intestate, the applicant shall so state and allege in his application or any amendment thereof and such persons and their heirs or devisees shall thereupon be included and considered as defendants to such application under the term and designation, "all other persons, if any, having any right or interest in or lien upon land or any part thereof described herein," or under the designation, "unknown heirs, and devisees of __________" as the case may require, and notified by publication as provided in section 5309.15 of the Revised Code. When the place of residence or post-office address of any person, whose residence or post-office address is required to be given, is unknown, it shall be so stated and alleged, if the applicant also alleges that upon diligent inquiry and research, stating of what such inquiry and research consisted, he has been unable to ascertain such residence or address. Thereupon such person shall be notified by publication as provided in such section, as one whose residence and post-office address are unknown.
If any person named as a defendant is known by the plaintiff to be under disability of any kind, that fact and the nature thereof, and the name, place of residence, and post-office address of the guardian or trustee of such person shall be stated in the application or an amendment thereof, or reason given for the omission of such information.
The probate court or the court of common pleas may order an application to be amended in any particular, not inconsistent with sections 5309.02 to 5310.21, inclusive, of the Revised Code, but all amendments shall be in writing signed and sworn to the same as the original.
R.C. §5309.12