Oklahoma is a state located in the South Central region of the United States of America. With an estimated 3,687,050 residents in 2009 and a land area of 68,667 square miles (177,847 km²), Oklahoma is the 28th most populous and 20th-largest state. The state's name is derived from the Choctaw words okla and humma, meaning "red people", and is known informally by its nickname, The Sooner State. Formed by the combination of Oklahoma Territory and Indian Territory on November 16, 1907, Oklahoma was the 46th state to enter the union. Its residents are known as Oklahomans, and its capital and largest city is Oklahoma City.