Mo. Rev. Stat. § 66.070

Complaints filed alleging violation of a county ordinance may include any number of persons charged with the same offense, and no proceedings shall be dismissed or defendant discharged by reason of any informality or irregularity in any complaint; but such complaint may, by leave of the court, at any time before or during the trial prior to the retirement of the jury or the findings of the judge, be amended without prejudice to the proceedings.