S.D. Codified Laws § 11-2-37
If an area within a county and not within a municipality becomes so situated that a zoning ordinance or any other purpose or procedure set forth in this chapter is advisable, persons within the area may apply to the board to establish or enlarge the area as a special zoning area or the board may on its own initiative establish or enlarge the area as a special zoning area, pursuant to this chapter. No special zoning area may be formed in a county in which a county wide comprehensive plan and zoning ordinances have been adopted. The formation of a special zoning area is only valid in a county that has not adopted a county wide comprehensive plan and zoning ordinances. The board may establish or enlarge a special zoning area on its own initiative if the special zoning area comprises an area of at least five square miles.
SDCL 11-2-37