Mont. Code Ann. § 70-27-203

On the trial of any proceeding for any forcible entry or forcible detainer, the plaintiff is only required to show, in addition to the forcible entry or forcible detainer complained of, that the plaintiff was peaceably in the actual possession at the time of the forcible entry or was entitled to the possession at the time of the forcible detainer. The defendant may show in defense that the defendant or the defendant's ancestors or those whose interest in the premises the defendant claims have been in the quiet possession of the premises for the space of 1 whole year before the commencement of the proceedings and that the defendant's interest in the premises is not then ended or determined, and the showing is a bar to the proceedings.