There are 3 US Post Offices in Mellette County serving a total of 1,992 residents equating to 664 residents per post office. It's estimated that approximately 3,179 packages are handled across the 3 county post offices annually. Mellette County is a county located in the U.S. state of South Dakota. As of the 2010 census, the population was 2,048. Its county seat is White River. The county was created in 1909 and organized in 1911. It was named by European-American settlers after Arthur C. Mellette, the last Governor of the Dakota Territory and the first Governor of the state of South Dakota. Historically territory of the Sioux/Lakota peoples, 33.35 percent of the county's land is trust land associated with the Rosebud Indian Reservation in the neighboring county to the south. According to the U.S. Census in 2000, 52.2% of the population is Native American, mostly the federally recognized Sicangu Oyate (Upper Brul\u00e9 Sioux) and the Rosebud Sioux Tribe, a branch of the Lakota people."