Ohio State Route 339 runs north from a point just west of Belpre, Ohio, and Parkersburg, West Virginia, branching out to areas of southern Noble County. This is west of Marietta and Interstate 77. To be precise, the southern end of Ohio Route 339 occurs at Ohio Route 618, just south of an expressway carrying US Route 50, Ohio Route 7, and Ohio Route 32. Ohio Route 339's first recourse is to proceed through a complete interchange with that expressway. Then, it continues north through the middle of Washington County. It passes through Waterford and Beverly, and then it begins angling northeast. Ohio Route 339 clips the southeastern corner of Morgan County before entering Noble County. This northwest angle is the final stretch of Ohio Route 339, which ends at Ohio Route 821 near Dexter City.