Mo. Rev. Stat. § 231.010: County commissions to divide counties into road districts.

The county commissions of all counties, other than those under township organization, shall, during the month of January, 1918, with the advice and assistance of the county highway engineer, divide their counties into road districts, all to be numbered, of suitable and convenient size, road mileage and taxable property considered. Said commissions, during the month of January biennially thereafter, have authority to change the boundaries of any such road district as the best interest of the public may require.