Rapid City (Mni Lúzahaŋ Otȟúŋwahe; "Swift Water City") is the second most populous city in South Dakota in the US and the county seat of Pennington County. Named after Rapid Creek, where the settlement developed, it is in the western part of the state, located on the eastern slope of the Black Hills mountain range. The population was 67,956 as of the 2010 Census.