Mo. Rev. Stat. § 542.170

If the persons assembled, as indicated herein, shall fail to disperse without unnecessary delay, the following associate circuit judges shall each, in the order in which they are herein named, have power and authority to require the aid of a sufficient number of persons in arms or otherwise, and to proceed as they may deem expedient, and to repress and disperse such riotous assemblage and arrest offenders. That is to say, the duty of requiring the aid of such force and directing its employment shall devolve, in the first instance, on the mayor of the town or city in which such assemblage occurs, and if he be not present or be unable to act, then on the judge of any court of record, the sheriff, the marshal, or the coroner. In case of the absence of any of the officers mentioned in this section, the officers named after him herein shall have all the power and authority which such absentee would have had if present.