Illinois River

About

Jolliet–Marquette and Starved Rock. The Illinois begins near Joliet and runs 273 miles to its mouth at Grafton, where it meets the Mississippi. Along the way it crosses seventeen counties, from Grundy and La Salle in the north down through Peoria, Mason, and Fulton, to Jersey and Calhoun at the confluence. Its watershed drains more than 18 million acres and reaches into over half of Illinois's counties, making it one of the state's defining waterways. USGS streamgage 05568500 anchors the modern hydrological record, averaging roughly 16,300 cubic feet per second, with an optimal paddling window between 8,200 and 24,500 CFS.

The river's recorded history opens in 1673, when Louis Jolliet and Father Jacques Marquette canoed down the Mississippi and returned up the Illinois. Marquette called it "our route," and it became the basis of French Canada's fur trade network. Starved Rock, now a National Historic Landmark on the river, was the site of the 1763 Battle of Starved Rock, where the Illinois Confederation destroyed Pontiac's village. Before European contact, the river flowed through the ancestral territory of Indigenous peoples, serving as a primary travel corridor, hunting ground, and gathering place; the 1800s-era treaties, the 1830 Indian Removal Act, and the 1840s–1890s allotment era established the cession framework.

The nineteenth century brought industry. From the 1830s through the 1920s, the watershed was logged to support the regional timber industry of the 1850s–1910s and the railroad expansion of the 1860s–1910s. Local sawmills, logging drives, and downstream lumber operations were the major operators until the 1910 exhaustion of the old-growth stands, the 1915 start of state forestry conservation, and the 1930s establishment of state forests ended large-scale logging. Meanwhile, engineers began reshaping the channel itself: the first lock and dam rose at Henry, in Marshall County, taming the current for commercial barges.

The river's character changed again in 1900, when the opening of the Chicago Sanitary and Ship Canal linked the Great Lakes to the Illinois and sent water levels into significant flux. That engineered connection still defines the river today, binding the Great Lakes to the Mississippi system through a corridor that carries both the weight of commerce and the life of an inland basin.

Science followed the industry. The 1870s–1890s USGS survey, the 1880s–1910s establishment of gauging stations, and the 1910s–1930s state geological survey streamflow assessments were the first comprehensive hydrological studies of the river. Later, the 1950s–1970s state water pollution control studies and the 1972–2000 Clean Water Act assessments addressed more than a century of logging, agricultural, and industrial impacts. Since 2010, the Illinois DNR, working with local watershed partnerships, has pushed recovery forward — streambank stabilization from 2015 to 2024, native fish restocking from 2017 to 2024, nutrient reduction strategy implementation from 2018 to 2024, and water-quality improvements from 2020 to 2024. Today the Illinois carries a State designation and is recognized as an Illinois Fishing River, a place where the layered history of a heavily worked watershed still shares the current with its recovering ecology.