The fact that Illinois is intersected by several long-distance transportation routes has been of central importance in the state's economic development for a century and a half. East access by way of the major rivers and the Great Lakes system facilitated extensive migration to Illinois even before the coming of the railroads in the 1850s. Most of the nation's rail lines converge on Illinois, and Chicago and St. Louis (especially East St. Louis) have been the two main US railroad centers since the late 19th century. Interstate highways, notably the main east-west routes, also cross the state, and Chicago's central location in the United States has made it a major transfer point for airline connections.
After several false starts in the 1830s and 1840s, the state's railroad system was begun in the 1850s. The Illinois Central aided by the first federal land grants, opened up the prairie lands in the years before the Civil War. By 1890, about 10,000 mi (16,000 km) of track crisscrossed the state, placing 90% of all Illinois farms no more than 5 mi (8 km) from a rail line. The railroads stimulated not only farming but also coal mining, and in the process created tens of thousands of jobs in track and bridge construction, maintenance, traffic operations, and the manufacture of cars, rails, and other railroad equipment.
The rise of automobile and truck traffic in the 1920s and 1930s dealt the railroads a serious blow, but their utter ruin was staved off by complex mergers that incorporated bankrupt or threatened lines into ever-larger systems. By 1974, the state had 10,607 mi (17,070 km) of track, 2nd only to Texas. Shedding their unprofitable passenger business in the 1970s (except for important commuter lines around Chicago that were taken over by public agencies), the railroads concentrated on long-distance freight traffic. The bankruptcy of the Penn Central, Rock Island, and Milwaukee Road systems during the 1970s impelled some companies, notably the Illinois Central Gulf and the Chicago & North Western, to shift their attention to real estate and manufacturing. Abandoned railroad tracks and right-of-ways were reverting to the private sector in the 1990s and being developed into public bicycle trails, walking paths, and greenways to take advantage of the scenic beauty of the state. There were 41 railroad companies operating 10,159 route mi (16,349 km) of track within the state in 2000. Chicago is the hub of Amtrak's passenger service, which operated approximately 20 train routes through Illinois in 1996. Total ridership through the state's 35 stations amounted to 2,526,721 that year.
Mass transit is of special importance to Chicago, where subways, buses, and commuter railroads are essential to daily movement. The transit systems were built privately but eventually were acquired by the city and regional transportation authorities. Ridership declines every year, as fewer people work in the central city and as more people choose the privacy and convenience of travel by automobile. Federal aid to mass transit, beginning in 1964, and state aid, initiated in 1971, have only partly stemmed the decline. Outside Chicago, transit service is available in some of the older, larger cities.
The road system of Illinois was inadequate until the 1920s, when an elaborate program to build local and trunk highways first received heavy state aid. In 2000, 138,372 mi (222,688 km) of public roadway served 9,168,095 registered vehicles—including 5,953,984 automobiles and 3,000,302 trucks—operated by 7,961,046 licensed drivers. The main east–west routes are I-90, I-88, I-80, I-74, I-72, I-70, and I-64. I-94 links Chicago with Milwaukee to the north and Indiana to the east, while I-57 and I-55 connect Chicago with the south and southwest (St. Louis), respectively.
Barge traffic along the Mississippi, Ohio, and Illinois rivers remains important, especially for the shipment of grain. The Port of Chicago no longer harbors the sailing ships that brought lumber, merchandise, and people to a fast-growing city. However, the port is still the largest on the Great Lakes, handling 23.9 million tons of cargo in 2000, mostly grain and iron ore. Midway Airport in Chicago became the world's busiest after World War II but was superseded by O'Hare Airport, which opened in the late 1950s. O'Hare lost its title as busiest airport in the world in March 2000 when it was superseded by Atlanta's Hartsfield International. With 612 airports and 253 heliports in 2002, Illinois is also an important center for general aviation.