Collar counties

Collar counties is a colloquialism for DuPage, Kane, Lake, McHenry, and Will counties, the five counties of Illinois that border Cook County, which is home to Chicago. The collar counties are part of the Chicago metropolitan area and comprise many of the area's suburbs. After Cook County, the collar counties are also the next five most populous counties in Illinois. According to the "Encyclopedia of Chicago", there is no specifically known origin of the phrase, but it has been commonly used among policy makers, urban planners, and in the media.
In 1950, the Census Bureau defined the Chicago metropolitan statistical area as comprising Cook County, four of the five collar counties (excluding McHenry), and Lake County in Indiana. In 2010, reflecting urban growth, the Bureau redefined the area as comprising several additional counties in Illinois, Indiana, and Wisconsin.
As of 2010, there are 3,143,257 people residing in the collar counties, nearly 25% of the population of Illinois. Cook County and the collar counties combined are home to approximately 65% of Illinois's population.
Use in political discussions.
While it is not its exclusive use, the term is often employed in political discussions. Like many other suburban areas in the United States, the collar counties have somewhat different political leanings from the core city. Chicago has long been a Democratic stronghold, while the collar counties historically tilted Republican. In recent elections, however, the collar counties have voted for Democrats, but with lower margins than Cook County. Because Cook County consistently votes in large proportions for Democrats, and downstate Illinois consistently votes overwhelmingly Republican, the collar counties are routinely cited as being the key to any statewide election. However, that conventional wisdom was challenged in 2010 as Democrat Pat Quinn won election as governor while only winning 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.
Barack Obama used the term in his speech before the Democratic National Convention in 2004.