Illinois
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The first is Northern Illinois, dominated by the Chicago metropolitan area, including the city of Chicago, its suburbs, and the adjoining exurban area into which the metropolis is expanding. The "collar counties" are the five counties that surround the centrally located Cook County in the Chicago metropolitan area: DuPage County, Kane County, Lake County, McHenry County, and Will County. 

As defined by the federal government, the Chicago metro area includes a few counties in Indiana and Wisconsin and stretches across much of northeastern Illinois, but not as far as Rockford, generally along Interstates 80 and 90. The region is cosmopolitan, densely populated, industrialized, and settled by a wide variety of ethnic groups. The term "Chicagoland" is sometimes used to describe the metro area, including Chicago, its suburbs within Cook County, and the so-called collar counties. The term is said to have been coined by Chicago Tribune publisher Robert R. McCormick [1]. The Chicagoland Chamber of Commerce defines it as all of Cook, and DuPage, Kane, Lake, McHenry and Will counties. [2]
The Quad Cities Metropolitan Area is on both sides of the Mississippi River separating Illinois from Iowa. The Illinois side includes Henry County, Mercer County, and Rock Island County. [3]

In extreme northwestern Illinois the Driftless Zone, a region of unglaciated and therefore higher and more rugged topography, occupies a small part of the state. Charles Mound, located in this region, is the state's highest elevation above sea level.

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