S.D. Codified Laws § 58-16-35
A policy of group life insurance shall contain a provision that the validity of the policy may not be contested, except for nonpayment of premiums, after it has been in force for two years from its date of issue; and that no statement made by any person insured under the policy relating to the person's insurability may be used in contesting the validity of the insurance with respect to which such statement was made, after such insurance has been in force prior to the contest for a period of two years during such person's lifetime. No statement made by the group policyholder or any person insured under the group policy may be contested unless it is contained in a written instrument signed by that person. The two-year limitation for contesting the validity of the insurance for any person insured under the policy does not apply to fraud on the part of the applicant or insured.
SDCL 58-16-35