Chicago, officially the City of Chicago, on Lake Michigan in Illinois, is one of the largest cities in the United States. As of the 2017 census-estimated population of 2,716,450, Chicago is the third most populous city in the United States after New York and Los Angeles, and 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 and fourth largest in North America. The city is the birthplace of the skyscraper, and considered 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.