1830s
- June 30, 1834
A large portion of unorganized land was added to Michigan Territory, corresponding to present-day Iowa, western Minnesota, and eastern North Dakota and South Dakota.
- March 2, 1836
The Republic of Texas declared independence from Mexico, claiming a Rio Grande boundary encompassing present-day West Texas, the majority of New Mexico, and portions of Colorado, Kansas, and Wyoming. Actual control extended over approximately the eastern half of present-day Texas. Miller County in Arkansas Territory now intruded on the borders of Texas, and the people there began to take a Texian identity, leading to both governments having representatives from the county.
- June 15, 1836
Arkansas Territory was admitted as the 25th state, Arkansas. It continued to claim Miller County, with increasing irrelevance.
- July 4, 1836
Wisconsin Territory was split off from Michigan Territory, consisting of present-day Wisconsin, Minnesota, Iowa, and eastern North and South Dakota. As an inducement to give up its claim over the Toledo Strip to Ohio, the whole of the present-day upper peninsula was assigned to Michigan Territory, giving it the present-day borders of Michigan.
- January 26, 1837
Michigan Territory was admitted as the 26th state, Michigan.
- March 28, 1837
The Platte Purchase added a small area of land to Missouri, giving it its present-day boundaries.
- July 4, 1838
Iowa Territory was split off from Wisconsin Territory, consisting of present-day Iowa, western Minnesota, and eastern North Dakota and South Dakota, leaving Wisconsin Territory with northeastern Minnesota and Wisconsin.
Read more about this topic: Territorial Evolution Of The United States