Chicago, officially the City of Chicago, is the third most populous city in the United States, after New York City and Los Angeles. 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 saw the creation of 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.
Chicago was incorporated as a city in 1837 near a portage between the Great Lakes and the Mississippi River watershed and grew rapidly in the mid-nineteenth century. After the Great Chicago Fire of 1871, which destroyed several square miles and left more than 100,000 homeless, the city made a concerted effort to rebuild.