The Wisconsin River is a tributary of the Mississippi River in the U.S. state of Wisconsin. At approximately 430 miles (692 km) long, it is the state's longest river. The river's name, first recorded in 1673 by Jacques Marquette as "Meskousing", is rooted in the Algonquian languages used by the area's American Indian tribes, but its original meaning is obscure. French explorers who followed in the wake of Marquette later modified the name to "Ouisconsin", and so it appears on Guillaume de L'Isle's map (Paris, 1718). This was simplified to "Wisconsin" in the early 19th century before being applied to Wisconsin Territory and finally the state of Wisconsin.