Missouri River Course: Seven U.S. States, No International Borders

The Missouri River, North America's longest river at 2,341 miles (3,767 km), flows entirely within the United States through seven states:

1. Montana — Headwaters at Three Forks (Jefferson, Madison, Gallatin confluence); 680 mi in state
2. North Dakota — 350 mi; Lake Sakakawea (Garrison Dam), Lake Oahe
3. South Dakota — 310 mi; Lake Oahe, Lake Sharpe, Lake Francis Case, Lewis & Clark Lake
4. Nebraska — 180 mi (forms NE-SD border, then NE-IA border); channelized
5. Kansas — 120 mi (NE-KS border); channelized, leveed
6. Iowa — 150 mi (IA-NE border, IA-MO border); Loess Hills
7. Missouri — 430 mi (longest state segment); crosses state west-east; joins Mississippi at St. Louis

Key Features

• Dams/Reservoirs: 6 mainstem dams (Pick-Sloan Plan) — Fort Peck, Garrison, Oahe, Big Bend, Fort Randall, Gavins Point
• Major Tributaries: Yellowstone, Platte, Kansas, Osage, Grand, Chariton
• Navigation: 735 mi maintained channel (Sioux City to mouth) — barge traffic (grain, fertilizer)
• Basin: 1.37M km² (529,000 sq mi) — 1/6 of continental US; 10 states, 2 Canadian provinces (Saskatchewan, Alberta — via Milk River tributary)

International Note

While the Missouri's basin extends into Canada (Milk River → Alberta/Saskatchewan), the river itself does not cross any international border. It is a wholly domestic US waterway, unlike the Red River (north to Hudson Bay) or Columbia River (Canada to US).