S.D. Codified Laws § 58-16-19
The premium for insurance under § 58-16-18 shall be paid by the policyholder, either from the employer's or union's funds or funds contributed by the employer or union, or from funds contributed by the insured employees or members, or from both. If any part of the premium is to be derived from funds, contributed by the insured employees or members, the insurance with respect to spouses and children may be placed in force only if at least seventy-five percent of the then eligible employees or members, excluding any as to whose family members evidence of insurability is not satisfactory to the insurer, elected to make the required contribution. If no part of the premium is to be derived from funds contributed by the employees or members, all eligible employees or members, excluding any as to whose family members evidence of insurability is not satisfactory to the insurer, must be insured with respect to their spouses and children.
SDCL 58-16-19