Mississippi Territory was was a historic, organized territory of the United States from April 7, 1798, and expanded twice (in 1804 and 1812), until it extended from the Gulf of Mexico to the southern border of Tennessee. (Georgia gave up the northern portion in 1802, and the Gulf Coast region was acquired from Spain following the War of 1812.) Originally Mississippi Territory included what is now Alabama, and just before Mississippi was admitted into the Union in 1817, the Alabama Territory to the east was separated out. On December 10, 1817, Mississippi was admitted to the Union as the 20th state.
The Mississippi Territory was organized in 1798 from land that had been disputed by the U.S. and Spain until Spain ceded claim with Treaty of Madrid in 1795. This area extended from 31 degrees and 32 degrees 28' north latitude, or approximately the southern half of the present states of Alabama and Mississippi.
The state of Georgia maintained a claim over almost the entire area of the present states of Alabama and Mississippi (from 31 to 35 degrees north latitude) until it surrendered its claim in 1802. Two years later, Congress extended the boundaries of the Mississippi Territory to included all of the Georgia cession.
In 1812 Congress annexed to the Mississippi Territory the Mobile District of West Florida, claiming that it was included in the Louisiana Purchase, although Spain disputed this and maintained its claim over the area. In the following year General James Wilkinson occupied this district with a military force, the Spanish commandant offering no resistance.
In 1817 the Mississippi Territory was divided, when the western portion became the state of Mississippi, and the eastern became the Alabama Territory, with St. Stephens, on the Tombigbee River, as the temporary seat of government.
See also: Historic regions of the United States, History of Alabama, West Florida, Yazoo lands