Coordinates: 47°24?49?N 111°28?43?W? / ?47.41361°N 111.47861°W? / 47.41361; -111.47861 Smith River is a tributary of the Missouri River, in central Montana, in the United States. It rises in southern Meagher County in the Castle Mountains and flows northwest in the valley between the Big Belt and Little Belt mountains, past White Sulphure Springs and past Smith River State Park. It turns north-northwest (NNW), and is joined by Hound Creek in Cascade County, and joins the Missouri approximately 9 miles (14 km) southwest of Great Falls.