Mont. Code § 25-3-602
The acceptance by a nonresident of the rights and privileges conferred by the laws of this state to use the highways, roads, and streets of the state and its political subdivisions, as evidenced by the nonresident operating a motor vehicle on the highways, roads, and streets, is considered equivalent to and construed to be an appointment by the nonresident of the secretary of state of the state of Montana to be the nonresident's true and lawful attorney upon whom may be served all lawful summonses and processes against the nonresident growing out of any accident, collision, or liability in which the nonresident may be involved while operating a motor vehicle upon the highways, roads, and streets. The acceptance or operation is a signification of the nonresident's agreement that any summons or process against the nonresident that is served on the secretary of state is of the same legal force and validity as if served on the nonresident personally within the state of Montana.
§ 25-3-602, MCA