S.D. Codified Laws § 46A-4-95
All irrigation districts, created under the provisions of this chapter, and any addition to or deletion from any such district, heretofore established or purporting to be established or adjusted pursuant to the provisions of this chapter and chapters 46A-5 to 46A-7, inclusive, and having a de facto existence of at least one year, are hereby declared to be valid and legally created political subdivisions of the state. The regularity and validity of the creation of the irrigation districts or any boundary adjustments of the districts are not open to question in any court in this state. All acts and proceedings of any such irrigation district or of its board of directors, or both, leading up to the authorization and execution of an existing contract between any such irrigation district and the United States of America, and all acts and proceedings of any such irrigation district or of its board of directors, or both, leading up to the issuance and deliverance of bonds of any such irrigation district are hereby legalized, ratified, confirmed, and declared valid to all intents and purposes. All such existing contracts and outstanding bonds are hereby legalized and declared to be valid and legal obligations of and against the irrigation district executing or causing the execution of the contracts or bonds.
SDCL 46A-4-95