Northern Commonwealth

The Northern Commonwealth was one of the thirteen commonwealths of the pre-War United States of America.

Background
Created in 1969, it was comprised of the former states of Montana, Wyoming, North Dakota, and South Dakota. Both before and after the war, Highway 89 passes through the area and is used for travel. The commonwealth bordered the country of Canada and the Northwest, the Four States, the Plains, and Great Midwest Commonwealths.

Former Wyoming
In 2281, the Great Khans could have abandoned the Mojave, and worked with the Followers of the Apocalypse in Wyoming to create a mighty empire. Also, the White Legs can flee to Wyoming after their leader, Salt-Upon-Wounds, is killed. The region is described as a vast wilderness, and it experiences harsh winters.

Former Montana
Montana was the location of a Brotherhood of Steel bunker, the Lonesome Drifter was born here, and there were coal mines active in the area. If the Courier has the Lady Killer perk, it is revealed he may have had a child with a woman from there.

Former South Dakota
In Fallout 4, MacCready mentions a warehouse in South Dakota while searching warehouses in Goodneighbor, saying "Some strange things turn up in these places, ever hear about that warehouse in South Dakota? Yeesh." Mount Rushmore is also mentioned as being located in South Dakota.

Appearances
The Northern Commonwealth is mentioned only in Fallout 3, and Fallout: New Vegas and its add-on Honest Hearts. South Dakota's Mount Rushmore appears in the Atomic Command game in Fallout 4 and is mentioned in the Fallout 76 Wild Appalachia update.