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, 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". With small mountain ranges, prairie, and eastern forests, most of Oklahoma lies in the Great Plains and the U.S. Interior Highlands.