S.D. Codified Laws § 12-4-18
The clerk of courts shall, within fifteen days after the close of each month, prepare an abstract from the records of the names of persons declared mentally incompetent in the preceding month. The clerk of courts shall send the name of a person declared mentally incompetent to the county auditor of the county in which the person declared incompetent resides.
The county auditor shall remove from the master registration list:
The county auditor shall match voter registration records maintained in or transmitted to the statewide voter registration file with the death records maintained as vital statistics records by the Department of Health, the social security death index, the Social Security Administration master death file, and the records of felony convictions maintained by the Unified Judicial System each month. Any voter identified as deceased, as mentally incompetent, or who is serving a sentence for a felony conviction must be removed from the voter registration records.
The State Board of Elections shall promulgate rules, pursuant to chapter 1-26, determining how voter registration records are matched.
Prior to providing a registration list to precincts, as prescribed in § 12-4-10, the county auditor must certify with the secretary of state that all individuals required to be removed from the master registration list have been removed based on the information available to the county auditor at the time the certification is submitted. The State Board of Elections shall promulgate rules, pursuant to chapter 1-26, prescribing the form to certify the accuracy of the master registration list.
SDCL 12-4-18