Okmulgee County is a county located in the U.S. state of Oklahoma. As of the 2010 census, the population was 40,069. The county seat is Okmulgee. Formerly part of the Creek Nation, the county was created at statehood in 1907. The name Okmulgee is derived from the Hitichita (Lower Creek) word okimulgi, meaning "boiling waters".