Oklahoma ( ; Choctaw: Oklahumma, pronounced [oklahómma]; Cherokee: ᎣᎧᎳᎰᎹ, Okalahoma, pronounced [ògàlàhǒːmã́]) is a state in the South Central region of the United States, bordered by the state of Texas to the south and west, Kansas to the north, Missouri to the northeast, Arkansas to the east, New Mexico to the west, and Colorado to the northwest. Partially in the western extreme of the Upland South, it is the 20th-most extensive and the 28th-most populous of the 50 United States. Its residents are known as Oklahomans and its capital and largest city is Oklahoma City.The state's name is derived from the Choctaw words okla, 'people' and humma, which translates as 'red'. Oklahoma is also known informally by its nickname, "The Sooner State", in reference to the Sooners, settlers who staked their claims in the Unassigned Lands before the Indian Appropriations Act of 1889 authorized the Land Rush of 1889.

The land now known as Oklahoma has been inhabited since at least the last ice age. The Southern Plains villagers and the Mississippian people inhabited the area between roughly 800 and 1500. The Southern Plains Panhandle culture developed in the Oklahoma Panhandle in western Oklahoma while the Caddoan Mississippian culture inhabited the eastern parts of the state and included the major settlement of Spiro Mounds. The area was also inhabited by the Wichita people, Tonkawa people, and Caddo people. Between 1300 and 1500, the Plains Apache migrated into the Southern Great Plains (now western Oklahoma). During the 1700s, the Comanche people, Kiowa people, Osage people, and Quapaw people migrated into the region.

The first European contact with the region was the Spanish explorer Francisco Vázquez de Coronado in 1541. However, the land was claimed by the Kingdom of France's Louisiana colony and included in the Louisiana Purchase to the United States in 1803. Oklahoma was part of District of Louisiana (1804–1805), Louisiana Territory (1805–1812), Missouri Territory (1812–1821), Arkansas Territory (1819–1828), before finally being designated Indian Territory. In the 1830s, the United States began forcibly removing Native Americans to Indian Territory, with the most famous instance being the deportation of the Five Civilized Tribes (Cherokee, Chickasaw, Choctaw, Muscogee, and the Seminole) which became known as the Trail of Tears. During the American Civil War, the Five Tribes formally sided with the Confederate States of America, while some tribal members served in the Union-aligned Indian Home Guard. After the American Civil War, slavery was abolished by treaty in the Five Tribes. Between 1866 and 1899, the cattle trails from Texas to Kansas ran through the territory. The Dawes Act of 1887 began the allotment of most Oklahoma tribes and the Curtis Act of 1898 authorized the allotment of the Five Tribes territory. The Indian Appropriations Act of 1889 authorized the Land Rush of 1889 in the Unassigned Lands of Indian Territory. In 1890, Oklahoma Territory was formed out of the western half of Indian Territory. After an attempt to make Indian Territory into the State of Sequoyah failed in 1905, Oklahoma Territory and Indian Territory were merged into the State of Oklahoma when it became the 46th state to enter the union on November 16, 1907.

The 20th century discovery of petroleum led to the development of a powerful oil industry. In the 1910s and 1920s, Oklahoma experience major instances of civil unrest with the Green Corn Rebellion and the Tulsa Race Massacre. In the 1930s, the Dust Bowl led to mass emigration from the state. Conservation efforts in the state reversed population declines in 1950 and continued through the 1960s. In 1995, the state was the site of one of the largest domestic terror attacks, the Oklahoma City Bombing. In the 21st century, the United States Supreme Court ruled in McGirt v. Oklahoma that the Muscogee Nation reservation was never disestablished. The ruling led to similar rulings regarding the other Five Tribes (Cherokee Nation, Choctaw Nation, Chickasaw Nation and Seminole Nation of Oklahoma).