Route 27 begins at an intersection with US 1 in the village of Mystic, within the town of Stonington.

North of I-95 it becomes Whitehall Avenue then becomes Main Street as it runs through the village of Old Mystic in the town of Groton.

[1] Route 27 from the intersection of Jerry Browne Road (milepost 2.13) in Stonington to the Route 184 terminus (milepost 3.21) in Groton is a state designated scenic road.

This portion of the route provides a view to the Mystic River, which it closely parallels.

The old Route 27 followed the path of the Colonel Ledyard Highway.