Mo. Rev. Stat. § 64.510: County commission may provide for county plan, when — county planning commission (second and third class counties).

The county commission of any county of the second or third class may, after approval by vote of the people of the county, provide for the preparation, adoption, amendment, extension and carrying out of a county plan for all areas of the county outside the corporate limits of any city, town or village which has adopted a city plan in accordance with the laws of the state. Upon the adoption of the county plan there is created in the county a county planning commission as hereinafter provided.