The Chicago Portage was a short overland route between the Chicago River and the Des Plaines River that allowed travelers to move between the Great Lakes and the Mississippi River system, making it a crucial low crossing of the continental divide between Atlantic and Gulf of Mexico watersheds. French explorers Father Jacques Marquette and Louis Jolliet recorded and used this route while exploring North America’s interior. In their era, the crossing passed through the seasonally changing Mud Lake, a wetland that later disappeared. The preserved western end in Lyons, Illinois, now protects this historically important passage and interprets its role in continental travel.