Ohio Rev. Code § 5541.02
The board of county commissioners shall determine, from the statistics and information furnished by the several boards of township trustees within the county, the relative importance and value for traffic of the various public highways of the entire county. The board of county commissioners shall begin work as soon as the necessary information is furnished by the several boards of township trustees within the county and, after a careful review and consideration of the information furnished, shall select and designate a connected system of county highways, of the mileage it deems proper and expedient, connecting with the intercounty and state highways of the county all of the villages and centers of rural population within the county. The system of highways, when selected and designated by the board of county commissioners, shall be known as the system of county highways of the county, and all of the roads composing the system shall be known and designated as county roads. The board of county commissioners may call to its assistance the county engineer and may require the county engineer to report as to the relative importance of the highways of any township, with respect to which the board of township trustees fails to report within a reasonable time. Upon the completion of its investigation and the designation of a system of county highways, the board of county commissioners shall require the engineer to make a map of it. A copy of this map, with the mileage of the selected roads indicated on it, together with a brief statement by the board of county commissioners of its reasons for the selection made, shall be transmitted to the director of transportation.
If the director finds that the system has been designated in substantial compliance with this section and section 5541.01 of the Revised Code, and that all portions of the system of county highways connect with either a state or intercounty highway, or another county road, the director shall, within sixty days, approve the system and certify the approval to the board of county commissioners, which shall cause a copy of the map, approved by it, to be made a part of its records and shall cause a copy of it to be filed in the office of the county engineer and of the fiscal officer of each township within the county. The system of roads designated upon the map shall then become the system of county roads of the county. Each road constituting a part of the system shall be given a number by the board of county commissioners, which may also divide the roads into convenient sections and assign appropriate designations to each section. No state or intercounty highway or part of it shall be included in the system of county highways. The board of county commissioners may make changes in or additions to the county system as in the manner provided by this section. All expenses incurred in carrying out this section shall be paid from the general county road fund.
R.C. §5541.02