Mo. Rev. Stat. § 64.100

64.100. Division of unincorporated territory into districts — regulation (certain first class counties). — For any or all of said purposes, the unincorporated territory may be divided into districts of such number, shape, and area as may be deemed best suited to carry out the purposes of sections 64.010 to 64.160 and shall be shown upon the plan; and within such districts, the erection, construction, reconstruction, alteration, repair or use of buildings, structures or land may be regulated and restricted. All such regulations shall be uniform for each class or kind of buildings or land uses throughout each district, but the regulations in one district may differ from those in other districts. The regulations shall be made in accordance with a comprehensive plan, and shall give reasonable consideration, among other things, to the character of the district, its suitability for particular uses, conserving the value of buildings and of existing development, and encouraging the most appropriate use of land throughout the county.

(L. 1941 p. 481 § 9)