Mont. Code § 71-3-1004
A person, corporation, or partnership claiming a lien under this part shall file with the county clerk of the county in which the land, leasehold, or pipeline or some part of the land, leasehold, or pipeline is situated a statement verified by affidavit setting forth the amount claimed and the items of the claim, the dates on which labor was performed or material or services furnished, the name of the owner of the leasehold or pipeline, if known, the name of the claimant and the claimant's mailing address, a description of the leasehold or pipeline, and if the claimant is a claimant under 71-3-1003, the name of the person for whom the labor was immediately performed or the material or services were immediately furnished. The statement must be filed within 6 months after the date upon which the material or services were last furnished or labor was last performed under contract.
§ 71-3-1004, MCA