Lake Andes is a city in, and the county seat of, Charles Mix County, South Dakota, United States. The population was 710 at the 2020 census. …Lake Andes is a city in, and the county seat of, Charles Mix County, South Dakota, United States. The population was 710 at the 2020 census. The town took its name from Lake Andes which some say derives its name from a pioneer hunter named Handy, while others believe was named after Edward Andes, a fur company official. The town and the lake are referred to as Bde Ihaƞke in Dakota language of the native Yankton Sioux Tribe.