State Route 31 (SR 31) is a 32.12-mile-long (51.69 km) Ohio State Route that runs between the Marysville and Kenton in the US state of Ohio. The southern terminus of SR 31 is at an intersection with SR 38 in downtown Marrysville and the northern terminus is at an intersection with U.S. Route 68 (US 69), in downtown Kenton. None of the highway is listed on the National Highway System.