State Route 31 (SR 31) is a 32.12-mile-long (51.69 km) Ohio State Route that runs between Marysville and Kenton in the US state of Ohio. The southern terminus of SR 31 is at an intersection with SR 38 in downtown Marysville and the northern terminus is at an intersection with U.S. Route 68 (US 68), in downtown Kenton. None of the highway is listed on the National Highway System. Most of the route is a rural two-lane highway and passes through both farmland and residential properties.

State Route 38 is a south–north state highway in the state of Ohio. Its southern terminus is near Bloomingburg and Washington Court House at the U.S. Route 62 / SR 3 concurrency and its northern terminus is in Marysville at the intersection of 5th Street and Main Street where the road continues north as SR 31.