S.D. Codified Laws § 34A-5-52
All sanitary sewer districts, established pursuant to chapter 34A-5, and having a de facto existence of one year or more by December 31, 1979, are declared to be valid and legally created subdivisions of the state. The validity and regularity of the creation of these sanitary districts may not be open to question in any court in this state, and all acts and proceedings of any such sanitary district or the board of trustees, or both, including those proceedings leading up to the authorization and execution of contracts between any such sanitary district and the United States of America as of December 31, 1979, are hereby legalized, ratified, confirmed, and declared valid to all intents and purposes. All completed or existing contracts, including outstanding bonds as of December 31, 1979, are hereby legalized and declared to be valid obligations of and against the sanitary district executing or causing the execution and issuance of them.
If any person has any vested right or rights affected by this section, and action or proceeding to enforce such right or rights is not commenced prior to January 1, 1981, such right or rights shall be forever barred, and no action or proceeding so brought may have any force or effect, or may be maintained in any court of this state.
SDCL 34A-5-52