S.D. Codified Laws § 14-2-38
A school board of any school district may contract with any board of public library or joint library trustees for provision of any or all school library services. If twenty percent or more of the cost of providing these combined school and public library services shall be borne by the school district, then the school board may annually appoint additional members to the board of public library trustees in proportion to the school district's part of the total funds made available during each year by both parties for the combined school and public library services, for the purchase of school and public library materials, and for the provision and maintenance of quarters for the combined library; provided, however, that the school board shall not appoint more than seven members to the board.
SDCL 14-2-38