S.D. Codified Laws § 7-2-8
The board of county commissioners of each of the counties comprising the newly consolidated county shall, after the proclamation of consolidation by the Governor, meet in joint session at the county seat of the county that had the largest population before consolidation on the first Monday in July following the proclamation. The commissioners shall divide the new county into three to seven commissioner districts, numbering them consecutively, complying as nearly as possible with the provisions of the law regulating the districting of counties into commissioner districts, or provide that the commissioners are elected at large, if so designated in the study committee's county consolidation plan. The commissioners shall set the length of the initial term for each of the new commissioner districts to be either two or four years, so that all succeeding regular elections have, insofar as practicable, the same number of vacancies to be filled. The commissioner districts established pursuant to this section must remain the same unless changed pursuant to § 7-8-3 or 7-8-10.
SDCL 7-2-8