S.D. Codified Laws § 5-9-23
The deferred payments for lands sold and the interest thereon shall be paid promptly when due to the commissioner of school and public lands. Whenever the purchaser of any tract shall fail to pay the principal and interest due by him to the state for such tract within three months after same shall become due or shall violate any of the provisions of the contract of sale, such contract shall be null and void and he shall forfeit the amount of purchase money and interest paid on the purchase of said land, and all right, title, and interest in all improvements thereon, and such payments and improvements shall be retained by the state for the same purposes for which the proceeds of sale from such lands are used, in full satisfaction and in liquidation of all damages for the use and possession of said property by the purchaser; and the state shall have immediate right to reenter and take possession of said real estate.
SDCL 5-9-23