Mont. Code § 81-8-311
Whenever it is necessary for an officer or person charged with the service of process out of any of the courts of this state to take possession of any cattle or horses running at large and commonly known as range stock, between November 1 and the next succeeding May 15, it is a sufficient service of such process for the officer or person within 15 days after receiving the process for service to file a copy thereof with the county clerk of the county wherein such property is running at large, with a notice appended thereto stating the number as near as may be and a description of the stock by marks and brands, and stating that such property or a portion thereof, as the case may be, is attached or levied upon in pursuance of such process. Such officer or person shall make due return of the service of process.
§ 81-8-311, MCA