Mellette is a city in Spink County, South Dakota, United States. The population was 199 at the 2020 census. Mellette was laid out in 1881…Mellette is a city in Spink County, South Dakota, United States. The population was 199 at the 2020 census. Mellette was laid out in 1881, and named in honor of Governor Arthur C. Mellette. According to the United States Census Bureau, the city has a total area of 0.26 square miles, all land.