Todd County is a county in the U.S. state of South Dakota. As of the 2020 census, the population was 9,319. Todd County does not have its own county seat. Instead, Winner in neighboring Tripp County serves as its administrative center. Its largest city is Mission. The county was created in 1909, although it remains unorganized. The county was named for John Blair Smith Todd, a delegate from Dakota Territory to the United States House of Representatives and a Civil War general.

A county seat is an administrative center, seat of government, or capital city of a county or civil parish. The term is in use in five countries: Canada, China, Hungary, Romania, and the United States. An equivalent term, shire town, is used in the U.S. state of Vermont and in several other English-speaking jurisdictions. County towns usually serve a similar function in Ireland, Jamaica, and the United Kingdom.