Okmulgee is a city in Okmulgee County, Oklahoma, United States. The population was 13,022 at the 2000 census. It is the county seat of Okmulgee County. The town has been the capital of the Muscogee (Creek) Nation since the United States Civil War. Okmulgee means "boiling waters" in the Creek language. The site was chosen because of the nearby rivers and springs.