Mo. Rev. Stat. § 242.580: Drainage tax, when delinquent — penalty.

All taxes provided for in sections 242.010 to 242.690 remaining unpaid after December thirty-first of the year for which said taxes were levied shall become delinquent and bear a penalty of one percent per month on the amount of said taxes from date of delinquency until paid. In computing said penalty each fractional part of a month shall be counted as a full month.