The Smith River is a tributary of the Missouri River, , approximately 100 mi (161 km) long, in west 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 NNW, and is joined by Hound Creek in Cascade County, and joins the Missouri approximately 12 mi (19 km) southwest of Great Falls.
