Its western terminus is in Lewis and Clark State Park.

Route 138 begins on the south shore of Lewis and Clark Lake in the community of Lewis and Clark Village within Lewis and Clark State Park, where the road continues east as Lake Shore Drive.

From the beginning point, the route heads southwest on two-lane undivided Lake Shore Drive, passing fields and woods in the state park.

The road turns to the east and becomes Lakecrest Boulevard, intersecting Lake Shore Drive again.

[1] The entire route is in Lewis and Clark Village, Buchanan County.