"A registered agent is: 1) an individual who resides in this state and whose business office is identical to the registered office; 2) a domestic corporation or not-for-profit domestic corporation whose business office is identical to the registered office; 3) a foreign corporation or not-for-profit foreign corporation authorized to transact business in this state whose business office is identical to the registered office. 4) a domestic limited liability company whose business office is identical to the registered office, or; 5) a foreign limited liability company authorized to transact business in this state whose business office is identical to the registered office."
http://sos.mt.gov/Business/FAQ.asp