Mont. Code Ann. § 7-3-4207

Petitions provided for in this part must be signed by only legal voters of the city. Each petition must contain, in addition to the names of the petitioners, the street and house number in which the petitioner resides and the petitioner's length of residence in the city. The petition must also be accompanied by the affidavit of one or more legal voters of the city stating that the signers of the petition were, at the time of signing, legal voters of the city and the number of signers at the time that the affidavit was made.