Oklahoma is a state in the South Central region of the United States. Oklahoma's the 20th-most extensive and the 28th-most populous of the fifty United States. The state's name is derived from the Choctaw words okla and humma, meaning "red people". Oklahoma's also known informally by Oklahoma's nickname, "The Sooner State", in reference to the non-Native settlers who staked their claims on land before the official opening date of lands in the western Oklahoma Territory or before the Indian Appropriations Act of 1889, which dramatically increased European-American settlement in the eastern Indian Territory. 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.