Mont. Code Ann. § 25-2-124

The proper place of trial for the recovery of a penalty or forfeiture imposed by statute is the county where the cause or some part thereof arose, except that when it is imposed for an offense committed on a lake, river, or other stream of water situated in two or more counties, the action may be brought in any county bordering on such lake, river, or stream and opposite to the place where the offense was committed.