Mont. Code Ann. § 7-12-2181

The board of county commissioners of any county in the state which may create any rural special improvement district or districts for any purpose may (in order to secure prompt payment of any special improvement district bonds or warrants issued in payment of improvements made therein and the interest thereon as it becomes due) create, establish, and maintain by resolution a fund to be known and designated as the rural special improvement district revolving fund. Nothing herein shall authorize or permit the elimination of a revolving fund until all bonds and warrants secured thereby and the interest thereon have been fully paid and discharged.