S.D. Codified Laws § 11-11-83
If the authority defaults in the payment of principal or of interest on any bonds issued under this chapter after the bonds become due, whether at maturity or upon call for redemption, and such default continues for a period of thirty days, or if the authority fails or refuses to comply with the provisions of this chapter, or defaults in any agreement made with the holders of an issue of bonds of the authority, the holders of twenty-five percent in aggregate principal amount of the bonds of such issue then outstanding, by instruments filed in the Office of the Secretary of State and proved or acknowledged in the same manner as a deed to be recorded, may appoint a trustee to represent the holders of such bonds for the purposes provided in § 11-11-84.
SDCL 11-11-83