Entering the town of Machias, SR 191 turns north and runs along the Machias River to US 1 where it runs southwest concurrently with it.

After 0.09 miles (0.14 km) concurrent with US 1, SR 191 branches off and heads to the northeast.

It then crosses a river flowing into the Hadley Lake.

As SR 191 continues north, it runs along Lake Cathance in Meddybemps.

Notably, in Cooper, SR 191 heads due east just below the 45 degree North parallel, possibly due to concerns in the 19th century that the Canada–United States border would be set there, as it is in New York and Vermont.