Mo. Rev. Stat. § 234.160
If a bridge be necessary over any watercourse which divides one county from another, and the county commissions of both counties shall determine that such bridge cannot be built, reconstructed or maintained at the expense of said counties, respectively, on account of the lack of funds and power to raise funds, then said county commissions of said counties are authorized to unite in empowering and granting the right to such person, partnership or corporation as they shall think proper to build or reconstruct such bridge as a toll bridge in such a manner and upon such terms and conditions as shall be agreed upon by said county commission, and empower such person, partnership or corporation to charge, collect and receive such tolls as shall be determined as maximum tolls by the said county commissions of said counties at the time of empowering or granting said rights. Said person, partnership or corporation shall then build or reconstruct and maintain said bridge at their own expense; provided, this section shall not apply to bridges on state roads.
§ 234.160, RSMo