The southern terminus of SR 590 is at a signalized intersection with SR 12 in the village of Bettsville.

Its northern terminus is at a T-intersection with SR 2 just south of Ottawa National Wildlife Refuge, and approximately 5 miles (8.0 km) north of Rocky Ridge.

Along its path, SR 590 travels through portions of Seneca, Sandusky and Ottawa Counties.

Its original routing consisted of the following: the current SR 53 from its intersection with Seneca County Road 51 southwest of the unincorporated community of Old Fort to its intersection with Seneca CR 61; CR 61 from SR 53 to the current southern terminus of SR 590 at SR 12 in Bettsville; and the entirety of the current routing of SR 590.

[3][4] The portions of current SR 53 and CR 61 noted would only be designated as SR 590 for one year.