Its eastern terminus is at SR 13 approximately one mile (1.6 km) southwest of Jacksonville.

The highway starts out heading easterly along Green Run Road, and as a side street called Oakley Drive arcs out to the northeast, the state highway bends to the east, departs the village and enters into Dover Township.

SR 685 then bends back to the east, and as it turns more northeasterly, it passes Carr Bailey Road.

Continuing easterly, SR 685 passes a few homes amid the unincorporated community of Modoc, where it also intersects Koches Road.

The landscape opens up a bit as the highway runs northeasterly back into Trimble Township, with a few homes appearing along the way, along with some grassy knolls.