SDCL § 6-1-1: Local officer's interest in public purchase or contract unlawful--Contract void.

It shall be unlawful for any officer of a county, municipality, township, or school district, who has been elected or appointed, to be interested, either by himself or agent, in any contract entered into by said county, municipality, township, or school district, either for labor or services to be rendered, or for the purchase of commodities, materials, supplies, or equipment of any kind, the expense, price, or consideration of which is paid from public funds or from any assessment levied by said county, municipality, township, or school district, or in the purchase of any real or personal property belonging to the county, municipality, township, or school district or which shall be sold for taxes or assessments or by virtue of legal process at the suit of such county, municipality, township, or school district. Such contract shall be null and void from the beginning.