Chicago, officially the City of Chicago, is the third most populous city in the United States. With over 2.7 million residents, it is also the most populous city in both the state of Illinois and the Midwestern United States. It is the county seat of Cook County. The Chicago metropolitan area, often referred to as Chicagoland, has nearly 10 million people and is the third-largest in the United States.
It is the birthplace of the skyscraper and perhaps the most influential architectural city of the 20th century. Chicago created the first standardized futures contracts at the Chicago Board of Trade; today its successor has evolved into the largest and most diverse derivatives market in the world, generating 20% of all volume in commodities and financial futures.