Okmulgee is a city in Okmulgee County, Oklahoma, United States. The population at the 2010 census was 12,321 a loss of 5.4 percent since the 2000 census figure of 13,022. It has been the capital of the Muscogee (Creek) Nation since the United States Civil War. The name is from the Creek word oki mulgee which means "boiling waters" in English. Other translations put it as "babbling brook" or 'Effluvium'. The site was chosen because of the nearby rivers and springs.