The southern terminus is at PA 8 near West Liberty.

The northern terminus is at PA 38 in North Washington.

The road heads through a mix of farmland and woodland with some homes, reaching the residential community of Euclid.

Here, the route passes over the Canadian National's Bessemer Subdivision railroad line and turns east into forested areas with a few residences.

At this point, PA 138 turns north to form a concurrency with PA 308 on Main Street, heading into the borough of West Sunbury.