There are 3 US Post Offices in Moody County serving a total of 5,185 residents equating to 1,728 residents per post office. It's estimated that approximately 8,276 packages are handled across the 3 county post offices annually. Moody County is a county located in the U.S. state of South Dakota in the United States. The population was 6,486 at the 2010 census. Its county seat is Flandreau. The county is named for Gideon C. Moody."