S.D. Codified Laws § 8-11-8
Every civil township maintaining a debt service fund for the payment of outstanding bonds, shall keep the accumulations in such debt service fund deposited with lawful depositories or invested in registered warrants or bonds of any municipal or public corporation of the State of South Dakota, or bonds, notes, or other obligations issued by any federal land bank, federal intermediate credit bank, bank for cooperatives, or any or all of the federal farm credit banks, or obligations of the United States, or bonds of any joint stock land bank of the United States, or bonds or securities of any kind issued by the State of South Dakota and the interest accruing on such investment of the debt service fund shall be credited to such debt service fund. The board of any township may invest moneys in any debt service funds thereof in bonds or registered warrants of such township. Moneys in any debt service fund shall be invested only in such of the above-named securities as will become due and payable on or before the date when the bonds for the payment of which such debt service fund was created become due and payable, except bonds of the United States or of the State of South Dakota. When such debt service fund is invested in other bonds of such township, there shall be a levy of a tax upon the taxable property of such township of sufficient amount to pay the interest and also the principal thereof when due, and such tax when collected shall be returned to the debt service fund for that purpose.
SDCL 8-11-8