S.D. Codified Laws § 3-12C-805
The disability benefit for the first thirty-six months shall be equal to fifty percent of the member's final average compensation immediately preceding the date of disability, increased by ten percent of such compensation for each child to a maximum of four such children.
Starting with the thirty-seventh month, if the member is eligible for and receiving disability benefits from social security, the disability benefit from the system is equal to the greater of the amount paid during the first thirty-six months less the amount of primary social security or the amount of the member's unreduced accrued retirement benefit as of the date of disability. If the member's unreduced accrued retirement benefit is the greater, it is immediately payable by the system notwithstanding any other provisions to the contrary. In no event may the annual amount of a disability benefit be less than twenty percent of the compensation on which the initial disability benefit was based.
Starting with the thirty-seventh month, if the member is not eligible for and receiving disability benefits from social security, the disability benefit from the system is equal to the greater of twenty percent of the compensation on which the initial disability benefit was based or the amount of the member's unreduced accrued retirement benefit as of the date of disability. If the member's unreduced accrued retirement benefit is the greater, it is immediately payable by the system notwithstanding any other provisions to the contrary. The disability benefit shall be paid only in the form of monthly installments. The provisions of this section apply to any member whose application for disability benefits is received by the system prior to July 1, 2015.
SDCL 3-12C-805