The Territory of Missouri was an organized incorporated territory of the United States that existed from June 4, 1812,[1] until August 10, 1821. In 1819, the Territory of Arkansas was created from a portion of its southern area. In 1821, a southeastern portion of the territory was admitted to the Union as the State of Missouri, and the rest became unorganized territory for several years.
On March 2, 1819, all of the Missouri Territory directly south of the parallel 36°30' north, except the so-called Missouri Bootheel between the Mississippi River and the Saint Francis River north of the 36th parallel north, was designated the new federal Territory of Arkansaw. (The spelling of Arkansaw would be changed a few years later, although the proper pronunciation of the name would be debated until 1881). The southeastern portion of the remaining Missouri Territory was admitted to the Union as the 21st State of Missouri on August 10, 1821.
The remaining portion of the territory to the north, northwest, west and southwest, consisting of the present states of Iowa, Nebraska, and the Dakotas, most of Kansas, Wyoming, Montana, and parts of Colorado, Minnesota and New Mexico, effectively became reverted to the status of unorganized territory after 1821, when Missouri became the 21st state. Thirteen years later in 1834, the portion in the north and east of the upper Missouri River was attached to the Michigan Territory around the Great Lakes. Over time, various federal territories in the West were created in whole or in part from its remaining area of unorganized status, as follows:
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