Mont. Code Ann. § 13-10-611

The county official certifying the sheets or sections of a petition shall keep a copy of the sheets or sections certified in the official files of the official's office. The copies may be destroyed 3 months after the date the petition was certified unless a court action is pending on the sufficiency of the petition. If a court action is brought within 3 months after the date the petition is certified, the county official may destroy the files only after final disposition of the court action.