|Region of Illinois|
Clockwise from top left: Rialto Square Theater (Joliet), Downtown Crystal Lake, Moser Tower (Naperville), Old DuPage County Courthouse (Wheaton), Great Lakes Naval Training Station (North Chicago) and Downtown Aurora.
|Counties||DuPage, Kane, Lake, McHenry and Will.|
|Named for||Their mutual proximity to and surrounding of Cook County.|
|Population (2012 Estimate)|
|Time zone||CST (UTC−06:00)|
|• Summer (DST)||CDT (UTC−05:00)|
|Area code(s)||224, 331, 630, 779, 815, 847|
The collar counties are the five counties of Illinois that border on Chicago's Cook County. After Cook County, they are also the next five most populous counties in the state. The collar counties (DuPage, Kane, Lake, McHenry, and Will) are tied to Chicago economically, but like many other suburban areas in the United States, they have very different political leanings from the core city. Chicago has long been a Democratic stronghold, but the collar counties are known for being historically Republican strongholds, although they have recently become more politically diverse, with all of the collar counties except McHenry County voting for Hillary Clinton in the 2016 United States presidential election.
While the demographics of these suburban Chicago counties are fairly typical for American metropolitan areas, the term is apparently unique to this area. Also, because Chicago is so firmly entrenched in the Democratic column, and rural Downstate is so overwhelmingly Republican, the collar counties are routinely cited as being the key to any statewide election. However, that conventional wisdom was challenged by the fact that in 2010 Democrat Pat Quinn became governor while winning only Cook, St. Clair, Jackson and Alexander counties. All five collar counties went Republican, so the key to winning that gubernatorial election was simply winning Cook County, but by a wide enough margin to overwhelm the rest of the state.
As of 2010 there are 3,143,257 people residing in the collar counties, nearly 25% of the population of Illinois.
- Lake County, Indiana
- Chicago metropolitan area
- The St. Louis, Missouri Metro-East region of Illinois (Madison County, Illinois, St. Clair County, Illinois, Montgomery County, Illinois, Macoupin County, Illinois, Jersey County, Illinois, Bond County, Illinois, and Adams County, Illinois)
- Orange County, California
- Long Island
- "'Quinn-Brady race may be decided in collar counties". Chicago Sun-Times.
- "Why the Collar Counties are Trending GOP". NBC Chicago. Retrieved 13 September 2013.
- Illinois gubernatorial election, 2010
- Mount, Charles (30 May 1989). "Collar Counties Cutting Court Backlogs". Chicago Tribune. Retrieved 13 September 2013.