Depending on their viewpoint and the era during which they lived, early explorers and settlers considered Lake Michigan to be either a priceless water highway deep into the interior of North America or a 307 mile long barrier to western travel.
The earliest European explorers didn’t even know Lake Michigan existed, thanks to the antipathy towards the French by the Iroquois Confederacy. French adventurers explored and mapped Lake Superior in the 1630s, long before the Iroquois allowed them passage to discover there was great water highway to the south. Not until Marquette and Jolliet explored south along the western store of Lake Michigan in 1673 did its length become appreciated.
A decade later, René-Robert Cavalier de La Salle used Lake Michigan as the major route to his new commercial colony in Illinois. By doing so, the French were able to bypass the Ohio River route to the west, the northern reaches of which were controlled by the well-armed and organized Iroquois Confederacy and their British allies.
Until the end of the French and Indian War in North America in 1764, Lake Michigan was, literally, a French lake. French forts controlled the Straits of Mackinac, Green Bay, and periodically Chicago and the mouth of the St. Joseph River at the southern end of the lake.
After the era of French control, the British controlled the lake for only a decade and a half or so before the new United States wrested control of most of the Great Lakes during the Revolutionary War. The War of 1812, essentially a short, less successful, continuation of the Revolution, did manage to solidify U.S. control over the lakes.

Fort Dearborn at the mouth of the Chicago River in 1831, just a few years before the U.S. Army built a channel through the sandbar at the mouth of the Chicago River.
During the era of U.S. pioneer settlement, Lake Michigan became more an impediment than a help to settlement. That was because there was no harbor at the southern end of the lake. The rivers emptying into Green Bay gave access to the Mississippi River via portages to the Wisconsin River, but that left the interior of what would become Illinois difficult to reach. Sailing ships that arrived in Chicago had to lighter their cargoes using small boats to laboriously across the sandbar blocking the mouth of the shallow and sluggish Chicago River. The ships themselves, however, could not enter the river and so were unable to dock to ride out the storms that frequently blew up. As a result, ships had to quickly unload and get back out into the lake to avoid being driven ashore by rough weather.
Settlers that came west to Detroit, where there was a port, were hindered in heading overland to the Illinois prairies along the old Territorial Road by numerous bogs and swamps in Michigan and Indiana.
Not until the 1830s, when the U.S. Army Corps of Engineers dug a channel through the sandbar, was a true harbor created at Chicago. The new channel allowed ships to enter the Chicago River and safely dock, and also made unloading cargo a lot faster and less labor-intensive. Almost overnight, Chicago became a major Great Lakes port. In 1833, only four sailing ships called at Chicago. In 1834, after the first channel through the bar opened, 176 sailing vessels arrived.
Chicago’s position so far south allowed ships to carry grain from the prairie hinterland in the Des Plaines, DuPage, and Fox River valleys directly to the great eastern cities and return with goods ranging from finished products to lumber to build the great city that was taking shape along the lake shore.

According to the Library of Congress, this illustration shows some of the grain elevators on the Chicago River just as Chicago was becoming the premier grain transhipment point in the nation.
In an astonishingly short time, in fact, Chicago displaced St. Louis as the chief grain shipment center in the west. St. Louis was well located on the Mississippi, but that was a curse as well as a blessing. Grain elevators, when they were finally invented and then perfected, could not be safely located on the shore of the great river because of its frequent floods. Chicago, however, with its location on Lake Michigan and the slow, sluggish Chicago River, was not affected by flooding since the lake level remained constant. That meant grain elevators could be built along the Chicago River—and the riverbank was soon lined with the towering structures.
In the late 1840s, the Illinois and Michigan Canal was completed, linking Lake Michigan with the Illinois River—and from there the great Mississippi-Ohio-Missouri River system. The canal made shipping grain that much more efficient since it could be sent both south on the canal to the New Orleans market as well as east on the lakes to the New York market. In addition, the canal offered farmers living near its banks an easier shipping destination than hauling it overland all the way into Chicago.
At virtually the same time, railroads began to stretch west to Chicago and beyond, and the era of shipping cargo strictly via the lakes was over. Railroads that headed straight west from New York, Baltimore, and the other great eastern cities eventually met Lake Michigan, where they had to curve south to pass the end of the lake. And that made Chicago an even greater city. Not only was it still the lakes’ greatest port, but it quickly became the great rail center of the West.
With both ships and trains arriving in Chicago in large numbers, the population of the city and its hinterland quickly grew. It proved a boon for Kendall County, with new settlers able to cheaply and easily travel west from their old homes to Chicago and then undertake a short overland journey to the rich prairie lands along the Fox River. Once settlers arrived in the Fox Valley, they found themselves in an excellent location to easily get both their crops and livestock to the growing markets in Chicago and to take advantage of lower cost goods from raw lumber to finished clothing.
More than almost any other geographical feature, Lake Michigan has had the greatest long-term effect on the economic growth of Illinois throughout the history of the region. Although the lake is no longer the vital shipping link with the East it once was, its effect on rail and road transportation routes has guaranteed that Illinois will remain a U.S. economic powerhouse for the foreseeable future.