S.D. Codified Laws § 55-4-11
A corporate trustee which is subject to regulation and supervision by state or federal authorities may deposit with itself trust funds which are being held necessarily pending investment, distribution, or the payment of debts, provided it pays into the trust for such deposit such interest as it is required by statute to pay on uninvested trust funds, or, if there be no such statute, the same rate of interest it pays upon similar nontrust deposits, and maintains in its trust department as security for all such deposits a separate fund consisting of securities legal for trust investments and at all times equal in total market value to the amount of the deposits. But no such security shall be required to the extent that the deposit is insured or given a preference by any state or federal law.
SDCL 55-4-11