S.D. Codified Laws § 12-4-40
The secretary of state may use the statewide voter registration file to identify any duplicate voter registration within the state. If the secretary of state has determined that there is a duplicate voter registration, the secretary of state shall notify the county whose official master registration file contains the oldest duplicate registration and such county shall remove the person from the voter registration file. If the secretary of state has identified a potential duplicate voter registration, the secretary of state shall notify the person registered in the county whose official master registration file contains the oldest potential duplicate registration. The secretary of state shall notify such person in a manner consistent with the provisions of § 12-4-19.1.
SDCL 12-4-40