State Route 643 (SR 643, OH 643) is a two-lane north–south state highway in the central portion of Ohio, a U.S. state. The highway's southern terminus is at a T-intersection with State Route 83 north of Coshocton. Its northern terminus is at a T-intersection with the concurrency of State Route 93 north of the Baltic. A section of the route is part of a scenic byway.The route was commissioned in the late 1930s.