U.S. Geological Survey Geographic Names Information System: Mississippi River, Length: 2,340 miles (3,770 km), Source: 47°14′22″N 95°12′29″W﻿ / ﻿47.23944°N 95.20806°W﻿ / 47.23944; -95.20806 U.S. Geological Survey Geographic Names Information System: Missouri River, Length: 2,540 miles (4,090 km), Source: 45°55′39″N 111°30′29″W﻿ / ﻿45.92750°N 111.50806°W﻿ / 45.92750; -111.50806