Mo. Rev. Stat. § 49.170
Four terms of the county commission shall be held in each county annually, at the place of holding commission meetings therein, commencing on the first Mondays in January, April, July, and October. The county commissions may alter the times for holding their stated terms, giving notice thereof in such manner as to them shall seem expedient; provided, that in counties now containing or that may hereafter contain seventy-five thousand or more inhabitants, and where county commissions are now or may hereafter be held at more places than one and at other places than the county seat, the terms of the commission shall be held monthly and alternately at the county seat and such other place as may be provided for the holding of a meeting, and each monthly term shall commence on the first Monday in each month.
§ 49.170, RSMo