The Illinois River is a principal tributary of the Mississippi River

Mississippi River

The Mississippi River is the largest river system in North America. Flowing entirely in the United States, this river rises in western Minnesota and meanders slowly southwards for to the Mississippi River Delta at the Gulf of Mexico. With its many tributaries, the Mississippi's watershed drains...

, approximately 273 miles (439 km) long, in the State of Illinois. The river drains a large section of central Illinois, with a drainage basin of 28070 square miles (72,701 km²). This river was important among Native Americans

Native Americans in the United States

Native Americans in the United States are the indigenous peoples in North America within the boundaries of the present-day continental United States, parts of Alaska, and the island state of Hawaii. They are composed of numerous, distinct tribes, states, and ethnic groups, many of which survive as...

 and early French traders as the principal water route connecting the Great Lakes

Great Lakes

The Great Lakes are a collection of freshwater lakes located in northeastern North America, on the Canada – United States border. Consisting of Lakes Superior, Michigan, Huron, Erie, and Ontario, they form the largest group of freshwater lakes on Earth by total surface, coming in second by volume...

 with the Mississippi. The French colonial settlements along the river formed the heart of the area known as the Illinois Country

Illinois Country

The Illinois Country , also known as Upper Louisiana, was a region in what is now the Midwestern United States that was explored and settled by the French during the 17th and 18th centuries. The terms referred to the entire Upper Mississippi River watershed, though settlement was concentrated in...

.