originally “all of that part of the United States west of the Mississippi, and not within the States of Missouri and Louisiana, or the Territory of Arkansas.” Never an organized territory, it was soon restricted to the present state of Oklahoma, excepting the panhandle and Greer county. The Choctaw, Creek, Seminole, Cherokee, and Chickasaw tribes were forcibly moved to this area between 1830 and 1843, and an act of June 30, 1834, set aside the land as Indian country (later known as Indian Territory).

In 1866 the western half of Indian Territory was ceded to the United States, which opened part of it to white settlers in 1889. This portion became the Territory of Oklahoma in 1890 and eventually encompassed all the lands ceded in 1866. The two territories were united and admitted to the Union as the state of Oklahoma in 1907.