Seven States Border the Missouri River

The Missouri River's State Boundaries

The Missouri River, North America's longest river (2,341 mi), forms borders or flows through seven U.S. states from its Rocky Mountain headwaters to the Mississippi confluence:

1. Montana — Headwaters at Three Forks (Jefferson, Madison, Gallatin)
2. North Dakota — Forms NE border with Montana; Lake Sakakawea (Garrison Dam)
3. South Dakota — Forms SE border with ND; four reservoirs (Oahe, Sharpe, Francis Case, Lewis & Clark)
4. Nebraska — Forms entire eastern border with Iowa/SD; no dams, free-flowing
5. Iowa — Western border entirely Missouri River; Loess Hills scenic byway
6. Kansas — NE corner only (~120 km); Kansas City metro straddles river
7. Missouri — Crosses state eastward; joins Mississippi at St. Louis

Notable Exclusions

• Wyoming: Yellowstone/Yellowstone River → Missouri, but WY doesn't touch Missouri River
• Colorado: No — Arkansas/Platte/Rio Grande/Colorado River basins
• Minnesota: Mississippi headwaters, not Missouri

Historical Significance

• Lewis & Clark Expedition (1804-06) followed entire course
• Highway for westward expansion, steamboats, fur trade
• Six mainstem dams (Pick-Sloan Plan, 1944-66) transformed ecology
• 25% of US agricultural output from basin