The highway's northern terminus is at SR 19 about 3 miles (4.8 km) south of Green Springs.

Existing entirely within Seneca County's Adams Township,[1] SR 778 has an AADT of 1150.

[2] The route's short journey begins at the intersection of SR 101 and County Road 43 (CR 43), and travels north, taking over for the county road.

The two-lane connector route travels north, arriving at its endpoint at the intersection of SR 19 and CR 44.

[1] The entire route is in Adams Township, Seneca County.