S.D. Codified Laws § 51A-5-4
Any bank empowered by its articles of incorporation to do trust business, shall, before transacting any such business, deposit and keep on deposit with the division evidences of indebtedness acceptable to the director which are payable to bearer or recorded in the name of the division and which constitute readily marketable legal investments for funds held by a bank as fiduciary in the amount of one hundred thousand dollars. Such deposit shall be for the security of the trust creditors of such bank or trust company, and shall be in bonds or notes and mortgages on real property within this state worth double the amount secured thereby, or insured by the federal housing administration, or bonds of the United States, or any state of the United States that has not defaulted on its principal or interest within ten years, or any organized county or township or first or second class municipality or school district in this state or some other state, and upon which there has been no default in payment of interest or principal. Income from such securities shall belong to and be paid the bank or trust company as long as it continues to conduct its business in the ordinary course and so long as authorized by the director.
SDCL 51A-5-4