Mo. Rev. Stat. § 67.1974

The boundaries of the district may be expanded by the addition of either an adjacent unincorporated or incorporated area. Upon presentation of a petition to the board signed by two percent of registered voters residing in either the unincorporated or incorporated area adjacent to the district. If the board determines that expansion is in the best interest of the current district, then the board shall give written notice to the election authority in the county in which the unincorporated or incorporated area is located to call an election. The election authority shall submit a proposition to the residents of the unincorporated or incorporated area at a municipal or state primary or general election, or at a special election called for that purpose. Such election authority shall give notice as provided in chapter 115. The proposition shall be submitted to voters in the unincorporated or incorporated area in substantially the following manner: