Mont. Code Ann. § 71-1-210

71-1-210 . Period of mortgage -- renewal. A mortgage of real property made, acknowledged, and recorded as provided by the laws of this state is good against all from the time it is recorded until 8 years after the maturity of the entire debt or obligation secured and no longer unless the mortgagee or the mortgagee's heirs, executors, administrators, representatives, or assigns, within 60 days after the expiration of the 8 years, file in the office of the county clerk where the mortgage is recorded an affidavit setting forth the date of the mortgage, when and where recorded, the amount of the debt secured, and the amount remaining unpaid and that the mortgage is not renewed for the purpose of hindering, delaying, or defrauding creditors of the mortgagor or owner of the land. Upon the filing of the affidavit, the mortgage is valid against all persons for an additional 8 years.