Mo. Rev. Stat. § 204.666
An assessment authorized under sections 204.650 to 204.672, once determined and imposed, shall constitute a lien against such property until paid in full and shall not be affected by the existence or enforcement of any other liens or encumbrances, nor shall enforcement of an assessment lien have any effect on the validity or enforcement of any tax lien or lien established by mortgage or deed of trust. An assessment lien becomes delinquent when an assessment is not paid in full as prescribed by sections 204.650 to 204.672, or when one or more periodic installments imposed by the district for an assessment remain unpaid for a period of thirty days or more after notice of delinquency in payment is mailed to the last known owners of the property subject to assessment by regular United States mail and by certified mail, return receipt requested, at their last known address, provided by such owners to the district and to the occupant of property that is subject to assessment, if different from that of the owners. In the event any such user fee remains unpaid after thirty days of the mailing of any such notice, and in addition to any other remedy the district may have by statute or duly enacted regulation for the collection of delinquent amounts owed to the district, the district shall be entitled to petition the circuit court having jurisdiction to foreclose upon the assessment lien by special execution sale of the property subject to the assessment for the unpaid assessment plus reasonable attorney's fees, court costs, and other reasonable costs incurred by the district in collection. In any such suit, the district shall name all parties appearing of record to have or claim an interest in the property subject to the unpaid assessment and shall file a notice of lis pendens in connection with said action. In addition, the district may obtain a judgment against last known owners of the property for any deficiency in payment of the assessment and costs and fees made a part of the court's judgment.
§ 204.666, RSMo