The French had explored up the St. Lawrence River from Montreal to the Great Lakes by canoe, and explored the Great Lakes. From there, they discovered multiple routes from the Great Lakes Basin to the Mississippi Basin.

Probably they usually learned of these routes from local Indians, rather than through exploration.

The first route to the Mississippi Basin was from Green Bay, Wisconsin, on Lake Michigan, up the Fox River (portaging around some of the rapids), through Lake Winnebago on up the Fox, then a short portage to the Wisconsin River (where Portage, Wisconsin is now) and down that to the Mississippi. This was the route taken by Marquette and Jolliet (the first French to reach the Mississippi Basin from the Great Lakes, in 1673).

Marquette and Jolliet also discovered the second route on their return journey, when they went up the Illinois River to the Des Plaines River and then portaged to the Chicago River and thus to Lake Michigan. They learned of this route from Indians they encountered on the Mississippi.

The French eventually used three other main routes between the Great Lakes and Mississippi Basins. One was to leave Lake Michigan on the Eastern shore by going up the St. Joseph River, portaging to the Kankakee River, and thus to the Des Plaines, the Illinois and the Mississippi. Another route was from the Western tip of Lake Superior, up the St. Louis River and the East Savannah River, and then portaging into streams leading to the Mississippi. The third route (and last to be opened up) was from Fort Presque Isle on Lake Erie, south overland on a long portage to LeBoeuf Creek, down that to French Creek, down that to the Allegany River, thence the Ohio to the Mississippi. It was the French opening up of this route in the late 1740s, early 1750s that led to conflict with the British and the start of the French and Indian Wars.