Northern Commonwealth

The  was one of the thirteen commonwealths of the pre-war United States of America. Created in the early 21st century, it was comprised of the former states of Montana, Wyoming, North Dakota and South Dakota.

Wyoming Wasteland
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.

Montana Wasteland
Nothing much is known about this area, except that the Lonesome Drifter was born here, there are coal mines active in the area and, if the Courier has the Lady Killer perk, it is revealed he may have had a child with a woman from there.

Appearances
The Northern Commonwealth does not appear in any released Fallout games. One of its states, Wyoming, is mentioned in one of the Fallout: New Vegas endings regarding the Great Khans.