File:Canada-United States Border, Northwest Angle, Minnesota (42165559660).jpg

The Northwest Angle, known simply as the Angle by locals, and coextensive with Angle Township, is a part of northern Lake of the Woods County, Minnesota. Except for minor surveying errors, it is the only place in the contiguous United States north of the 49th parallel, which forms the border between the U.S. and Canada from the Northwest Angle westward to the Strait of Georgia (between the state of Washington and the province of British Columbia). The land area of the Angle is separated from the rest of Minnesota by Lake of the Woods, but shares a land border with Canada. It is one of only six non-island locations in the 48 contiguous states that are practical exclaves of the U.S. It is the northernmost township in Minnesota and contains the northernmost point in the contiguous 48 states. The unincorporated community of Angle Inlet is in the Northwest Angle.

Seventy percent of the land of the Angle is held in trust by the Red Lake Indian Reservation (Ojibwa).

Although the Angle is listed as one of several distinct regions of Minnesota, its total population was 119 at the 2010 census. The area is mostly water and the land is mostly forest.

Angle Township was designated as territory of the United States because negotiators of the initial Canada–U.S. border misunderstood the geography of the area. Benjamin Franklin and British representatives relied on the Mitchell Map of colonial American geographer John Mitchell, which did not indicate the source of the Mississippi River—thought to lie some distance to the northwest—or the true shape of Lake of the Woods, which was instead shown as roughly oval. The 1783 Treaty of Paris thus stated that the boundary between U.S. territory and the British possessions to the north would run "...through the Lake of the Woods to the northwestern-most point thereof, and from thence on a due west course to the river Mississippi..."

But the source of the Mississippi River, Lake Itasca (then unknown to European explorers), lies almost due south of Lake of the Woods, rather than north and west of it. Additionally, the irregular actual shape of the lake made the identification of its northwest corner difficult. A survey team led by David Thompson in 1824 mapped the lake and found four possibilities, but did not conclusively declare one location. In 1825, a German astronomer in British service, Dr. Johann Ludwig Tiarks, surveyed the lake. Tiarks identified two possibilities for the northwesternmost point on the lake, based on Thompson's maps: the Angle Inlet and Rat Portage. To determine which point was the most northwestern, he drew a line from each point in the southwest-northeast direction. If the line intersected the lake at any point, it was not the most northwestern point. Tiarks determined that the only such line that did not intersect the lake was at the edge of a pond on the Angle Inlet.

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