Harding County is a county in the U.S. state of South Dakota. As of the 2020 census, the population was 1,311, making it the third-least populous county in South Dakota. Its county seat is Buffalo. Harding County was established as a county in the Dakota Territory on March 5, 1881, but was not organized at that time. Its name recognized J. A. Harding, who had been Speaker of the House of Dakota Territory. Its boundaries were altered in 1883, in 1889, and in 1894.