Richelieu (rĭshˈəlō) [key], river, c.75 mi (120 km) long, issuing from the north end of Lake Champlain, near the N.Y.–Que. border, and flowing N across S Que. to the St. Lawrence River at Sorel. It is a link in the waterway connecting the Hudson and St. Lawrence rivers. Visited (1609) by Samuel de Champlain, the French explorer, the river was the route of early explorers. It was an important military corridor in the French and Indian War, in the American Revolution, and in the War of 1812. There are pulp and paper mills along its banks. Ft. Lennox National Historic Park is on Île-aux-Noix near St. Jean, Que.