minnehaha county is a county in south dakota in the united states. as of the 2010 census, 169,468 people lived there. it is the most populous county in south dakota. the county seat of minnehaha county is sioux falls. the county took its name from the sioux indian word "mnihaha" which means "rapid water" or "waterfall." the word is often incorrectly translated as "laughing water." the word was changed to its current spelling to make it easier to pronounce. minnehaha county is part of the sioux falls, sd, metropolitan statistical area.