Mont. Code Ann. § 76-15-528

Any special assessment made and levied to defray the cost and expenses of any of the work enumerated in this chapter, together with any percentages imposed for delinquency and for cost of collection, shall constitute a lien against the property upon which such assessment is levied from the date on which such assessment is levied. This lien can only be extinguished by payment of such assessment with all penalties, costs, and interest.