County roads in Ohio comprise 29,088 center line miles (46,813 km), making up 24% of the state's public roadways as of April 2015[update].

[11] The maximum speed limit for an undivided county road is 55 miles per hour (90 km/h) in an unincorporated area.

[13] On February 17, 1804, an act of the General Assembly gave boards of county commissioners the authority to open roads.

[5] Plank roads could be brought under county supervision beginning on January 25, 1861, and commissioners were authorized to build turnpikes on February 16, 1870.

[5] In the 1972 Ohio Manual of Uniform Traffic Control Devices (OMUTCD), revision 21, issued 1999, the standard county route shield was a white rectangle bearing a black legend; the blue pentagon was considered an alternative design for a system of important county roads.

[15] The blue pentagon became the standard in the 2003 edition of the MUTCD, relegating the white rectangle to an alternative status.

[4] For counties that do utilize county road markers, the Ohio Department of Transportation's Ohio Manual of Uniform Traffic Control Devices (OMUTCD) specifies two designs, the gold-on-blue pentagon found in the national MUTCD and an alternative black-on-white square also found in some other states.