Montana Title 25. Civil Procedure § 25-31-405. Designating unknown person as defendant

When the plaintiff is ignorant of the name or part of the name of a defendant, that defendant may be designated in the summons and in any other process or proceeding in the action by a fictitious name or by as much of the defendant's name as is known, adding a description identifying the person intended. The person designated must be regarded as a defendant in the action and as sufficiently described in the action for all purposes. When the defendant's name or the remainder of the defendant's name is known or becomes known, the justice before whom the action is pending shall amend the proceedings already taken by the insertion of the true or full name in place of the fictitious name or part of a name, and all subsequent proceedings must be taken under the name inserted.