S.D. Codified Laws § 34A-5-14.1
Each sanitary district shall be governed by a board of trustees elected at large, as provided in this chapter. Each board of trustees shall consist of an odd number of members and shall have at least three but not more than eleven members, as provided in this section.
If a sanitary district provides or is proposed to provide sewer or water facility connections to more than one thousand five hundred households, farms, businesses, or other entities, the board of trustees shall consist of at least five but not more than eleven members. If a sanitary district provides or is proposed to provide at least one thousand but not more than one thousand five hundred sewer or water facility connections, the board of trustees shall consist of at least five but not more than nine members. If a sanitary district provides or is proposed to provide at least five hundred but not more than one thousand sewer or water facility connections, the board of trustees shall consist of at least three but not more than seven members. If a sanitary district provides or is proposed to provide fewer than five hundred sewer or water facility connections, the board of trustees shall consist of at least three but not more than five members.
The number of trustees for a newly incorporated or consolidated sanitary district shall be specified in the order of incorporation issued under § 34A-5-7 or in the consolidation resolution issued under § 34A-5-46.
SDCL 34A-5-14.1