There are 4 US Post Offices in Walworth County serving a total of 5,595 residents equating to 1,399 residents per post office. It's estimated that approximately 8,930 packages are handled across the 4 county post offices annually. Walworth County is a county located in the U.S. state of South Dakota. As of the 2010 census, the population was 5,438. Its county seat is Selby. The county was created in 1873 and organized in 1883. It is named after Walworth County, Wisconsin."