Manufacturing in Illinois, concentrated in but not limited to Chicago, has always been diverse. Before 1860s, small gristmills, bakeries, and blacksmith shops handled what little manufacturing was done. Industry tripled in size in the 1860s, doubled in the 1870s, and doubled again in the 1880s, until manufacturing employment leveled off at 10–12% of the population. Value added by manufacture grew at a compound annual rate of 8.1% between 1860 and 1900, and at a rate of 6.3% until 1929.

In 1997, the value of shipments by manufacturers totaled $205 billion. Major industrial items that Illinois produced in 1999 included construction machinery, farm equipment, cellular phones, electrical house wares, commercial printing, metal coatings, appliances and containers, various industrial machinery, and cooking products.

By far the leading industrial center is Chicago, followed by Rockford, the East St. Louis area, Rock Island and Moline in the Quad Cities region, and Peoria.

As of 1997, there were 39 Fortune 500 companies headquartered in Illinois (the 3rd most in the nation), including some of the world's "100 best managed companies": Abbott Laboratories, Amaco, BP, Baxter International, Caterpillar, Deere & Co., Illinois Tool Works, Morton International, Motorola, and Sarah Lee.

Earnings of persons employed in Illinois increased from $247.9 billion in 1997 to $263.4 billion in 1998, an increase of 6.2%. The largest industries in 1998 were services, 28.6% of earnings; durable goods manufacturing, 12.0%; and finance, insurance, and real estate, 9.9%. Of the industries that accounted for at least 5% of earnings in 1998, the slowest growing from 1997 to 1998 was state and local government (9.8% of earnings in 1998), which increased 4.6%; the fastest was finance, insurance, and real estate, which increased 9.0%.