SDCL § 9-9-14: Board--Quorum--Majority vote for action.

A majority of all the commissioners on the board of commissioners constitutes a quorum to do business. If a seat on the board is vacant due to removal, resignation, death, or by operation of law, the quorum consists of the majority of all the remaining commissioners who are qualified to serve by election or appointment pursuant to chapter 9-13. The board may compel the attendance of any absentee under penalties as prescribed by ordinance.

No action of the board is effective unless upon a vote of a majority of all the members of the board.