Flandreau FLAN-droo is a city in and county seat of Moody County, South Dakota, United States. The population was 2,372 at the 2020 census…Flandreau FLAN-droo is a city in and county seat of Moody County, South Dakota, United States. The population was 2,372 at the 2020 census. It was named in honor of Charles Eugene Flandrau, a judge in the territory and state of Minnesota. He is credited with saving the community of New Ulm, Minnesota, from destruction during conflict with the Sioux tribe in 1862.