There are 6 US Post Offices in Lyman County serving a total of 3,659 residents equating to 610 residents per post office. It's estimated that approximately 5,840 packages are handled across the 6 county post offices annually. Lyman County is a county located in the U.S. state of South Dakota. As of the 2010 census, the population was 3,755. Its county seat is Kennebec."