State Route 239 or SR-239 is a 22-mile (35 km) long route that serves as a connection between State Route 51 at Clayton with U.S. Highway 29 in Aberfoil.

The southern terminus of SR-239 is located at its intersection with State Route 51 and State Route 198 in Clayton. From this point, the route travels in a westerly direction before making a turn to the northwest near the county line in route to its northern terminus at its intersection with U.S. Highway 29 in Aberfoil.