Mo. Rev. Stat. § 139.290
Wherever, in any county in this state, money has been collected under an illegal levy, the county commission of such county or counties is hereby authorized to refund the same by issuing warrants upon the fund to which said money had been credited, in favor of the person or persons who paid the same as shown by the collector's books; provided, that should the person in favor of whom any warrant or warrants are issued be dead or unable to appear in person, then the same shall be paid to his heirs or legal representatives; provided further, that said county commission or commissions may, in their discretion, refund, in addition to the money collected, interest which may have accrued upon the same, not to exceed six percent; provided further, that before any levy shall be considered illegal, it shall have been so declared by the supreme court of the state of Missouri; provided further, that the provisions of this section shall only apply to those counties in which the money collected under said illegal levy is either in the county treasury or within the control of the county commission; provided further, that the county commission so refunding said money shall specify the time in which said money shall be refunded, and all warrants left on hand after the expiration of such time shall be by said county commission cancelled, and the money and interest turned into the school fund of the county.
§ 139.290, RSMo