| Area |
Date |
Territorial Name |
Notes |
| East of the Divide |
1682 |
Louisiana (France) |
One of the five colonies of New France and included the entire Mississippi River basin. The area north of the Arkansas River was called Upper Louisiana. |
| East of the Divide |
2/10/1763 |
Louisiana (Spain) |
Treaty of Paris gave Spain control over the Mississippi basin west of the Mississippi River following the French and Indian War. |
| East of the Divide |
10/1/1800 |
Colony of Louisiana (France) |
France reacquired Louisiana from Spain in the secret Treaty of San Ildefonso in 1800. |
| East of the Divide |
4/30/1803 |
Louisiana Purchase |
The Louisiana Purchase involved the Mississippi Basin not including the area east of the Mississippi. The small portion of present-day Glacier NP and Blackfeet Reservation within the Hudson Bay basin was not included. The Milk River basin now in Alberta was included. |
| East of the Divide |
10/1/1804 |
District of Louisiana |
The Louisiana Purchase was divided into Orleans Territory and the District of Louisiana. |
| East of the Divide |
7/4/1805 |
Louisiana Territory |
The District of Louisiana achieved territorial status and was renamed Louisiana Territory. The seat of government was St. Louis. |
| East of the Divide |
1806 |
Upper Louisiana Territory |
The District of Arkansas was formed with the remainder of Louisiana Territory being renamed Upper Louisiana Territory. |
| East of the Divide |
6/4/1812 |
Missouri Territory |
Louisiana Territory was renamed Missouri Territory June 4, 1812 when Louisiana became a state. |
| East of the Divide |
10/18/1818 |
Missouri Territory |
Treaty of 1818 ceded lands north of the 49th parallel to Britain. Lands within the Hudson Bay basin south of the 49th parallel became part of Missouri Territory. This includes the small bit of Glacier MP and the Blackfeet reservation previously outside of Louisiana. |
| East of the Divide |
8/10/1821 |
Unorganized Territory |
When Missouri became a state, the remainder of the territory became known as Unorganized Territory. |
| East of the Divide |
5/30/1854 |
Nebraska Territory |
Nebraska Territory was formed from the northern two-thirds of the Unorganized Territory. The capital was Omaha. |
| East of the Divide |
3/2/1861 |
Dakota Territory |
Dakota Territory was split from Nebraska Territory. The capital was Yankton. |
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| West of the Divide |
Prior to 1818 |
Unclaimed Territory |
The area from the divide to the Pacific Ocean was uncharted wilderness not claimed by any country. |
| West of the Divide |
10/18/1818 |
Oregon Country |
Treaty of 1818 created Oregon Country as land occupied by both the United States and Britain. |
| West of the Divide |
6/18/1846 |
Unorganized Territory |
The Oregon Treaty eliminated Oregon Country and the lands south of the 49th parallel and west of the divide became Unorganized Territory |
| West of the Divide |
8/14/1848 |
Oregon Territory |
Oregon Territory was formed west of the divide |
| West of the Divide |
3/2/1853 |
Washington Territory |
Washington Territory split from Oregon Territory. A tiny piece of Montana remained in Oregon Territory west of the divide south of the 46th parallel (south of Darby). |
| West of the Divide |
2/14/1859 |
Washington Territory |
This tiny piece of Oregon Territory near Darby was put back into Washington Territory when Oregon became a state in 1859. |
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| East and West of the Divide |
3/4/1863 |
Idaho Territory |
Idaho territory created from Washington and Dakota territories. The first territorial capital was at Lewiston. |
| East and West of the Divide |
5/28/1864 |
Montana Territory |
Montana Territory was carved from Idaho Territory with the boundaries the same as present-day Montana |
| East and West of the Divide |
11/8/1889 |
State of Montana |
State of Montana formed November 8, 1889 with no boundary changes from the territory. |
