Indian Territory, also known as Indian Country, Indian territory or the Indian territories, was land set aside within the United States for the use of Native Americans. The general borders were set by the Indian Intercourse Act of 1834. It was more properly "Indian territory" (lower-case T) than "Indian Territory" (capital T) because the name referred to the unorganized lands set aside for Native Americans, as opposed to an organized territory meant for settlement by Europeans .

The Indian Territory had its roots in the British Royal Proclamation of 1763, which limited white settlement to Crown lands east of the Appalachian Mountains. Indian Territory was reduced under British administration and again after the American Revolution, until it included only lands west of the Mississippi River.

At the time of the American Revolution, many Native American tribes had long-standing relationships with the British, but a less developed relationship with the American rebels. After the defeat of the British, the Americans twice invaded the Ohio Country and were twice defeated. They finally defeated a Native American confederacy at the Battle of Fallen Timbers in 1794, imposing the unfavorable Treaty of Greenville, which ceded most of what is now Ohio, part of what is now Indiana, and the present day sites of Chicago and Detroit to the United States. The Indian Territory served as the destination for the policy of Indian Removal, a policy pursued intermittently by American presidents early in the nineteenth century, but aggressively pursued by President Andrew Jackson after the passage of the Indian Removal Act of 1830. The Five Civilized Tribes in the South were the most prominent tribes displaced by the policy, a relocation that came to be known as the Trail of Tears. The trail ended in what is now Arkansas and Oklahoma, where there were already many Native Americans living in the territory, as well as whites and escaped slaves. Other tribes, such as the Delaware, Cheyenne, and Apache were also forced to relocate to the Indian territory. The Five Civilized Tribes set up towns such as Tulsa, Ardmore, Tahlequah, Tishomingo, Muskogee and others, which often became some of the larger towns in the state. They also brought their African slaves to Oklahoma, which added to the African-American population in the state. These tribes fought on the side of the Confederacy during the American Civil War. Brigadier General Stand Watie, a Confederate commander of the Cherokee nation, became the last Confederate general to surrender in the American Civil War on 23 June 1865.

see Oklahoma Civil War Confederate Units

In time, the Indian Territory was gradually reduced to what is now Oklahoma; then, with the organization of Oklahoma Territory in 1890, to just the eastern half of the area. The citizens of Indian Territory tried, in 1905, to gain admission to the union as the State of Sequoyah, but were rebuffed by Congress and Administration who did not want two new Western states, Sequoyah and Oklahoma. Citizens then joined to seek admission of a single state to the Union. With Oklahoma statehood in November 1907, Indian Territory was extinguished.

Many Native Americans continue to live in Oklahoma, especially in the eastern part.