Oklahoma is a state located in the South Central region of the United States of America. With an estimated 3 751 351 residents as of the 2010 census and a land area of 68 667 square miles (177 847 kmĀ²) 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.