Todd existed as a former county from 1862 to 1899. Most was transferred to Nebraska in 1882, mainly to what was reported as Boyd County in 1890; remainder annexed to Gregory in 1899.
Todd was re-instantiated as a current county in 1909.
Todd County is a county located in the U.S. state of South Dakota. As of the 2010 census, the population was 9,612. Its largest city is Mission. Todd County does not have its own county seat. Instead, Winner in neighboring Tripp County serves as its administrative center. The county is named after John Blair Smith Todd (April 4, 1814 – January 5, 1872) who was a delegate from Dakota Territory to the United States House of Representatives and a general in the Union Army during the American Civil War. He was a cousin of Mary Todd Lincoln.
The county lies entirely within the Rosebud Indian Reservation and is coterminous with the main reservation (exclusive of off-reservation trust lands, which lie in four nearby counties). It is one of five South Dakota counties entirely within an Indian reservation. (The others are Corson, Dewey, Shannon, and Ziebach.) By per capita income, is the 5th poorest county in the nation.