S.D. Codified Laws § 9-43-104

Any assessment or installment under Plan One or Plan Two may be paid without interest to the municipal finance officer at any time within thirty days after the approval of the assessment roll. Thereafter, and before the due date of the first installment, the entire assessment remaining, or any number of installments, plus interest from the approval date to the date of payment may be paid to the municipal finance officer. After the due date of the first installment, if the installments that are due together with interest have been paid, any of the remaining installments not yet due may be paid without additional interest to the municipal finance officer. All installments paid before their respective due dates shall be paid in inverse order of their due dates.