The major cities of the region are, well, Chicago — period. None of the outlying cities remotely approach the size of this mammoth metropolis. But that's not to say that Chicagoland doesn't include other cities; other large ones include:
Cook County, where Chicago is located, is the largest county in Illinois and the second-largest in the United States (after California's L.A. County). With more than 5 million residents, its population is larger than that of most U.S. states; a little more than half of them live in the central city, with the rest in a chain of suburbs that surrounds Chicago on the north, west and south sides.
Lake County, in the northeast corner of the state, was once largely rural but has become increasingly suburban in recent years. Its largest city, Waukegan, is also the county seat. Its southeast is part of Chicago's affluent North Shore, including Highland Park and Lake Forest, one of the wealthiest communities in the state. Other Lake County towns include Libertyville, Gurnee, Buffalo Grove, Fox Lake and Long Grove.
Will County lies south of Cook and DuPage; its largest city and county seat is Joliet.
The Forest Preserve District of Cook County is responsible for the numerous open spaces ("forest preserves") around the county. These preserves range from heavily used parks with extensive roads and well-developed picnic areas, to relatively isolated expanses of land that are only really accessible on foot (or cross-country skis in Winter).
The Pickwick in Park Ridge is one of the true grand movie palaces remaining in the Chicagoland area.