There are 6 US Post Offices in Codington County serving a total of 27,180 residents equating to 4,530 residents per post office. It's estimated that approximately 43,382 packages are handled across the 6 county post offices annually. Codington County is a county located in the U.S. state of South Dakota. As of the 2010 census, the population was 27,227. Its county seat is Watertown. The county was created in 1877 and organized in 1878. It is named for Rev. George S. S. Codington, legislator. Codington County comprises the Watertown, SD Micropolitan Statistical Area."