Were North Dakota and Michigan Part of the 1818 Treaty with Great Britain?

Michigan: Yes (indirectly). The Treaty of 1818 (Convention of 1818) set the U.S.–British North America boundary at the 49th parallel from the Lake of the Woods westward to the Rocky Mountains. Michigan Territory (est. 1805) lay east of Lake of the Woods, so its northern border was defined by earlier treaties (1783 Paris, 1794 Jay) and the Webster–Ashburton Treaty (1842) which fixed the Lake Superior–Lake of the Woods segment. But the 1818 treaty established the longitude line that became Michigan's western territorial reference.

North Dakota: No. In 1818, the area of present-day North Dakota was part of the Louisiana Purchase (1803) but not yet organized as U.S. territory (became Dakota Territory 1861). The 1818 treaty's 49th parallel line ran through it, but U.S. sovereignty north of the 49th parallel (Pembina region) wasn't fully resolved until the 1842 Webster–Ashburton Treaty and later surveys.

Key Distinction

• 1818 Treaty: Set 49th parallel from Lake of the Woods to Rockies.
• 1842 Treaty: Fixed eastern segment (Lake Superior to Lake of the Woods) and clarified the Pembina/Red River valley.

So Michigan's borders were influenced by the 1818 treaty's western extension, while North Dakota's northern border was defined by it but not under U.S. control at the time.