State Route 173 (SR 173) is a 20.9-mile-long (33.6 km) route that stretches from the Lincolnville Ferry Terminal in Lincolnville at its southern end to SR 220 in Liberty at its northern end.

Now following Beach Road, SR 173 generally heads northwest through forested area paralleling Frohock Brook at first as it curves around hills of Camden Hills State Park.

The two routes together head into Lincolnville Center, the home of the administrative buildings of the town, on Main Street.

[2] At Bickfords Corner, SR 173 makes a sharp turn to the southwest to cross a small stream then travels west.

Along Stevens Pond Road, the route reaches Trues Pond Road and heads west through downtown Liberty as the town's main street.