The Chicago metropolitan area, or Chicagoland, is the metropolitan area associated with the city of Chicago, Illinois, and its suburbs. It is the area that is closely linked to the city through social, economic, and cultural ties.
There are several definitions of the area, including the area defined by the Office of Management and Budget (OMB) as the Chicago-Joliet-Naperville, IL-IN-WI Metropolitan Statistical Area (MSA), and the area under the jurisdiction of the Chicago Metropolitan Agency for Planning (CMAP) (a metropolitan planning organization). The population of the Chicago CSA (Combined Statistical Area) is over 9.8 million people.
The Chicago Metropolitan Statistical Area (MSA) was originally designated by the United States Census Bureau in 1950. It consisted of the Illinois counties of Cook, DuPage, Kane, Lake and Will, along with Lake County in Indiana. As surrounding counties saw an increase in their population densities and the number of their residents employed within Cook County, they met Census criteria to be added to the MSA. The Chicago MSA, now defined as the Chicago-Naperville-Elgin, IL-IN-WI Metropolitan Statistical Area, is the third largest MSA by population in the United States with a population of 10,055,638 (2009 estimate). The Chicago metro area is the largest in an emerging Great Lakes Megalopolis.
The Chicago MSA is further subdivided by state boundaries into the Chicago-Naperville-Joliet, IL Metropolitan Division, corresponding roughly to the CMAP region; the Gary, IN Metropolitan Division consisting of the Indiana counties of Lake and Porter, as well as two surrounding counties; and the Lake County-Kenosha County, IL-WI Metropolitan Division.
The 2012 estimated population total for the MSA is 9,522,434. A breakdown of the 2009 estimated populations of the three Metropolitan Divisions of the MSA are as follows: