S.D. Codified Laws § 7-3-1
If fifteen percent of the registered voters, based upon the total number of registered voters at the last preceding general election, residing in any portion consisting of not less than twenty-four congressional townships or any portion consisting of not less than one hundred million dollars of real property valuation of any organized county in this state shall petition the county commissioners of such county for division thereof and for the organization of a new county or counties, setting forth in the petition the lines upon which the petitioners desire such county to be divided and the boundaries of the proposed new county or counties, together with the name or names they desire to be given the proposed new county or counties in which such petitioners reside, the county commissioners of such county shall submit the question of the division of such county to the voters thereof at the next general election. Such petition must be filed with the county auditor not later than the first Monday in July of any general election year.
Each county shall, after division as prayed for in such petition, contain not less than twenty-four congressional townships or not less than one hundred million dollars of real property valuation, or no election may be ordered.
SDCL 7-3-1