The southern terminus of SR 339 is at SR 618 approximately 2 miles (3.2 km) west of Belpre, and less than 0.50 miles (0.80 km) south of the U.S. Route 50 (US 50)/SR 7/SR 32 expressway.

The highway's northern terminus is a T-intersection with SR 821 about 0.75 miles (1.21 km) south of Dexter City.

SR 339's routing takes it through portions of the counties of Washington, Morgan and Noble.

No portion of SR 339 is included within the National Highway System, a network of highways deemed most important for the economy, mobility and defense of the nation.

It was initially a spur route that ran along its present alignment from its northern terminus at SR 821, at the time a part of US 21, southwesterly to approximately its southern intersection with County Road 75 (CR 75) in southern Noble County.