When considering the 48 contiguous states of the USA, the northernmost U.S. state is Minnesota (the Angle Inlet of northern Minnesota at 49°23'N is north of the 49° boundary between the U.S. and Canada and well north of any point in Maine).

Penasse is an unincorporated community in Angle Township, Lake of the Woods County, Minnesota, United States. Penasse is located on Penasse Island in Lake of the Woods, in the northern part of Northwest Angle. Its location makes it the northernmost populated place in the contiguous United States. The community was named for Tom Penasse, a Native American from the area. It had a post office in the town from 1920 to 1969. The French built Fort Saint Charles nearby in 1732.

More Info: en.wikipedia.org