Mont. Code Ann. § 25-2-117

If there are two or more defendants in an action, a county that is a proper place of trial for any defendant is proper for all defendants, subject to the power of the court to order separate trials under Rule 42(b) of the Montana Rules of Civil Procedure. If an action with two or more defendants is brought in a county that is not a proper place of trial for any of the defendants, any defendant may make a motion for change of place of trial to any county which is a proper place of trial.