The western terminus of the route is at US 20 southwest of Pioneer, and the eastern terminus is at US 20 in Maumee, southwest of Toledo.

The route runs parallel to the Ohio Turnpike (Interstate 80/Interstate 90 [I-80/I-90]) for much of its length, and intersects the turnpike at exit 13 northeast of Montpelier in Holiday City.

US 20 and US 20A are never more than five miles (8.0 km) apart for the entire 50-mile (80 km) stretch through the Ohio farm country, as the mainline of US 20 takes the more northerly route.

[3][4] The current US 20A was designated U.S. Route 20S (US 20S) in 1932, which replaced State Route 271 (SR 271) which had run from US 20 south to Montpelier, truncated SR 107, joined SR 2, and followed a road formerly not on the state highway system through most of Lucas County.

)[2] In the 1950s, part of the road east of Swanton was abandoned to make way for Toledo Express Airport.