S.D. Codified Laws § 58-16-24
The debtors eligible for insurance under a policy issued under § 58-16-23 shall be all of the debtors of the creditor whose indebtedness is repayable either in installments or in one sum at the end of a period not in excess of eighteen months from the initial date of debt, or all of any class or classes thereof determined by conditions pertaining to the indebtedness or to the purchase giving rise to the indebtedness. The policy may provide that the term "debtors" shall include the debtors of one or more subsidiary corporations, and the debtors of one or more affiliated corporations, proprietors, or partnerships if the business of the policyholder and of such affiliated corporations, proprietors, or partnerships is under common control through stock ownership, contract, or otherwise. No debtor shall be eligible unless the indebtedness constitutes an irrevocable obligation to repay which is binding upon him during his lifetime, at and from the date the insurance becomes effective upon his life.
SDCL 58-16-24