Mont. Code Ann. § 10-3-603

In case of a vacancy on any board of county commissioners occurring during or following an enemy attack, if the judge or judges of the judicial district in which the vacancy occurs be not available to make the appointment then the district judges of all other judicial districts shall be authorized to make such appointment. Provided, however, that of the available judges in the state of Montana that judge who holds court in the county seat closest to the county seat where the vacancy occurs shall be responsible for making the appointment to fill the vacancy.