S.D. Codified Laws § 58-16-17
The premium for a policy issued under § 58-16-12 shall be paid by the trustees wholly from funds contributed by the employer or employers of the insured persons, or by the union or unions, or by both, or partly from such funds and partly from funds contributed by the insured persons. A policy on which part of the premium is to be derived from funds contributed by the insured persons specifically for their insurance may be placed in force only if at least seventy-five percent of the then eligible persons, excluding any as to whom evidence of insurability is not satisfactory to the insurer, elect to make the required contributions. A policy on which no part of the premium is to be derived from funds contributed by the insured persons specifically for their insurance must insure all eligible persons, or all except any as to whom evidence of individual insurability is not satisfactory to the insurer.
SDCL 58-16-17