Most of the road, approximately 31.2 miles (50.2 km), follows the Knox Trail, the historic route of General Henry Knox took to bring cannon from Fort Ticonderoga on Lake Champlain in New York to aid in ending the Siege of Boston in the winter of 1775–76.

The road passes Catamount Ski Area and the village of South Egremont before merging with Route 41, just west of Great Barrington.

The two pass Butternut Basin Ski Area before crossing the Appalachian Trail and entering Monterey.

From there, the road passes through Monterey, running parallel to and eventually crossing the Konkapot River near the center of town.

Once in Blandford, the road heads due east, passing Miller Swamp, Jackson Hill and Blair Pond before entering the town's center, at which point the road begins to runs parallel to the south of Interstate 90 (the Massachusetts Turnpike).