It is routed northwest-to-southeast through portions of Toombs and Tattnall counties.

SR 178 begins at an intersection with US 1/SR 4 (South State Street) in Lyons, in Toombs County.

It heads southeast through rural areas until it intersects SR 56, west of Reidsville.

The highway continues to the southeast and meets SR 147, near the Georgia State Prison.

Just prior to crossing over the Ohoopee River, SR 178 curves to the east and continues in that orientation until it meets its eastern terminus, an intersection with SR 121/SR 144/SR 169 southwest of Glennville.