When the proposed improvement is along or upon a county line or crosses such county line or extends as a continuous road from one county into or through one or more adjoining counties, the boards of county commissioners of the counties interested shall sit as a joint board.
Improvement on county line
Ohio Rev. Code Ann. § 5553.13, under Chapter 5553 | County Roads - Establishment; Alteration; Vacation.
Ohio Rev. Code Ann. § 5553.13