Salem is the county seat of McCook County, South Dakota, United States. The city's population was 1,325 at the 2020 census. The current may…Salem is the county seat of McCook County, South Dakota, United States. The city's population was 1,325 at the 2020 census. The current mayor is Shawn English. Salem was founded in 1880 and named after the postmaster's hometown of Salem, Massachusetts. Salem at one time was called Melas. This was to prevent confusion with the now non-existent community of Salena, South Dakota.