1850s
- September 9, 1850
The Compromise of 1850 divided the Mexican Cession and land claimed by Texas but ceded to the federal government in exchange for taking on its debts. The western portion was admitted as the 31st state, California, most of the rest was organized as Utah Territory and New Mexico Territory, and a small portion became unorganized land. New Mexico Territory consisted of most of present-day Arizona and New Mexico, as well as a southern portion of Colorado and the southern tip of Nevada. Utah Territory consisted of present-day Utah, most of Nevada, and portions of Colorado and Wyoming. A peculiarity appeared at this time, when a small strip of land north of Texas was not officially designated as part of any state or territory (Texas gave up this land due to a United States federal law based on the Missouri Compromise, which prohibited slavery above the 36°30' parallel of North latitude). This came to be called the Neutral Strip or "No Man's Land", which corresponds to the present-day panhandle of Oklahoma.
- March 2, 1853
Washington Territory was split from Oregon Territory, consisting of present-day Washington, northern Idaho, and the western tip of Montana, leaving Oregon Territory with all of Oregon, southern Idaho and a portion of Wyoming.
- December 30, 1853
The Gadsden Purchase added some land to New Mexico Territory, corresponding to the southernmost areas of present-day Arizona and New Mexico.
- May 30, 1854
Kansas Territory and Nebraska Territory were organized; the remaining unorganized land colloquially became known as Indian Territory. Kansas Territory consisted of present-day Kansas and eastern Colorado. Nebraska Territory consisted of present-day Nebraska, and parts of Colorado, Montana, North Dakota, South Dakota, and Wyoming. Indian Territory corresponds to eastern Oklahoma.
- May 11, 1858
The eastern portion of Minnesota Territory was admitted as the 32nd state, Minnesota. The remainder became unorganized.
- February 14, 1859
The western portion of Oregon Territory was admitted as the 33rd state, Oregon. The remainder was assigned to Washington Territory.
Read more about this topic: Territorial Evolution Of The United States