1810s
- April 1810
The Hawaiian islands are unified as the Kingdom of Hawaii.
- October 27, 1810
By proclamation of President James Madison, the United States annexed the Baton Rouge and Mobile Districts of Spanish West Florida, declaring them to have been part of the Louisiana Purchase. One month earlier, these had declared independence from Spain as the Republic of West Florida. The U.S. Army seized control by threat of force in December after 90 days of independence as a country.
- April 30, 1812
Most of the Territory of Orleans was admitted as the 18th state, Louisiana. The rest of the territory (the northwestern tip) was ceded to Louisiana Territory.
- May 12, 1812
The federal government annexed a part of West Florida, the Mobile District, to Mississippi Territory, making the territory correspond to present-day Alabama and Mississippi.
- June 4, 1812
Louisiana Territory, having the same name as a state, was renamed to Missouri Territory.
- April 17, 1813
Republican Army of the North captured San Antonio, Texas, assassinated the governor Manuel María de Salcedo, proclaimed Texas an independent nation, and issued Texas's first constitution on this date. Spanish forces recaptured the province later that year and executed any Tejanos accused of having Republican tendencies. By 1820 fewer than 2000 Hispanic citizens remained in Spanish Texas.
- December 11, 1816
The southern portion of Indiana Territory was admitted as the 19th state, Indiana. The remainder became unorganized.
- March 3, 1817
Alabama Territory was split from Mississippi Territory; both correspond to their present-day counterparts.
- December 10, 1817
Mississippi Territory was admitted as the 20th state, Mississippi.
- October 20, 1818
The Treaty of 1818 established the 49th parallel north west of the Lake of the Woods as the border with British-held lands, and Oregon Country was established as a shared land between the United States and United Kingdom. Oregon Country consisted of most of present-day Idaho and Oregon, all of Washington, and a portion of Montana, as well as the southern part of the Canadian province of British Columbia. The treaty transferred the Red River Basin to the United States, consisting of northwestern Minnesota, northeastern North Dakota, and the northeastern tip of South Dakota.
- December 3, 1818
The southern portion of Illinois Territory was admitted as the 21st state, Illinois. The remainder was reassigned to Michigan Territory. The unorganized lands which had been a part of Indiana Territory prior to the admission of Indiana as a state were also assigned to Michigan Territory.
- March 2, 1819
The southern part of Missouri Territory was organized as Arkansaw Territory, consisting of present-day Arkansas as well as part of Oklahoma. It was not officially spelled Arkansas until later.
- December 14, 1819
Alabama Territory was admitted as the 22nd state, Alabama.
Read more about this topic: Territorial Evolution Of The United States