The Chicago metropolitan area, or Chicagoland, is the metropolitan area that includes the city of Chicago, Illinois, and its suburbs. With an estimated CSA population of 9.9 million people and an MSA population of 9.5 million people, it is the third largest metropolitan area in the United States.The Chicago metropolitan area is one of the world's largest and most diversified economies, with more than four million employees and generating an annual gross regional product (GRP) of over $679.69 billion in 2017. The region is home to more than 400 major corporate headquarters, including 31 in the Fortune 500.There are several definitions of the area, including the area defined by the United States Office of Management and Budget (OMB) as the Chicago–Joliet–Naperville-Aurora, 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).