Mo. Rev. Stat. § 64.850
For the purpose of promoting health, safety, morals, comfort or the general welfare of the unincorporated portion of counties of the first class not having a charter form of government, or of counties of the second, third or fourth class to conserve and protect property and building values, to secure the most economical use of the land, and to facilitate the adequate provision of public improvements all in accordance with a comprehensive plan, the county commission of any county of the first class not having a charter form of government, or of any county of the second, third or fourth class may, after approval by vote of the people as provided in section 64.845, regulate and restrict, by order of record, in the unincorporated portions of the county, the height, number of stories, and size of buildings, the percentage of lots that may be occupied, the size of yards, courts and other open spaces, the density of population, the location and use of buildings, structures and land for trade, industry, residence or other purposes.
§ 64.850, RSMo