The Territory of Oklahoma was an organized incorporated territory of the United States that existed from May 2, 1890, until November 16, 1907, when it was joined with the Indian Territory under a new constitution and admitted to the Union as the state of Oklahoma.

The 1890 Oklahoma Organic Act organized the western half of Indian Territory and a strip of country known as No Man's Land into Oklahoma Territory. Reservations in the new territory were then opened to settlement in a series of land runs in 1890, 1891, and 1893.

Seven counties were defined upon the creation of the territory. They were originally designated by number and eventually became Logan, Cleveland, Oklahoma, Canadian, Kingfisher, Payne, and Beaver counties. The Land Run of 1893 led to the addition of Kay, Grant, Woods, Garfield, Noble, and Pawnee counties. The territory acquired an additional county through the resolution of a boundary dispute with Texas, which today is split into Greer, Jackson, Harmon, and part of Beckham counties.

The Indian Territory and the Indian Territories are terms that generally described an evolving land area set aside by the United States Government for the relocation of Native Americans who held aboriginal title to their land as a sovereign independent state. In general, the tribes ceded land they occupied in exchange for land grants in 1803. The concept of an Indian Territory was an outcome of the US federal government's 18th- and 19th-century policy of Indian removal. After the American Civil War (1861–1865), the policy of the US government was one of assimilation.

The term Indian Reserve describes lands the British set aside for Indigenous tribes between the Appalachian Mountains and the Mississippi River in the time before the American Revolutionary War (1775–1783).

Indian Territory later came to refer to an unorganized territory whose general borders were initially set by the Nonintercourse Act of 1834, and was the successor to the remainder of the Missouri Territory after Missouri received statehood. The borders of Indian Territory were reduced in size as various Organic Acts were passed by Congress to create incorporated territories of the United States. The 1907 Oklahoma Enabling Act created the single state of Oklahoma by combining Oklahoma Territory and Indian Territory, ending the existence of an unorganized unincorporated independent Indian Territory as such. Before Oklahoma statehood, Indian Territory from 1890 onwards consisted of the Cherokee, Choctaw, Chickasaw, Creek and Seminole tribes and their territorial holdings.

Indian reservations remain within the boundaries of US states, but largely exempt from state jurisdiction. The term Indian country is used to signify lands under the control of Native nations, including Indian reservations, trust lands on Oklahoma Tribal Statistical Area, or, more casually, to describe anywhere large numbers of Native Americans live.