It begins in the west at an intersection with SR 9, serving as a 4.1-mile (6.6 km) southern spur of the highway, to U.S. Route 1 (US 1) near Wells Beach.

It runs eastward, intersecting local roads as it heads towards the coastline.

SR 9B continues eastward until it intersects and ends at US 1.

However, in 1955 the concurrency was removed,[2] truncating SR 9B to its current terminus and reducing it to a spur.

The entire route is in Wells, York County.