The title of this article is ambiguous. For other meanings, see Chicago (disambiguation).

Chicago (less commonly in German also Chikago, pronunciation: [ʃɪˈkɑːgoʊ]; Audio-Datei / Hörbeispiellisten? /i) is a city on the southwestern shore of Lake Michigan in the state of Illinois in the United States of America. With a population of 2,716,450, it is the third largest city in the United States. The agglomeration is home to 8.7 million people, and the Chicago metropolitan area to 9.7 million (2007).

Chicago has been an important commercial city in the United States since the mid-19th century. This function is aided by its status as a railroad hub and its location at the mouth of the Illinois Waterway. The city lies on important railroads connecting the east and west coasts and is linked to the Atlantic Ocean and to New York City by the Great Lakes and the Saint Lawrence Seaway or Erie Canal. The Illinois Waterway connects to the Gulf of Mexico via the Mississippi River.

Chicago is home to the Chicago Mercantile Exchange, the largest commodity futures exchange in the United States, and the Chicago Board of Trade, the largest commodity, futures and options exchange in the United States. It is also home to the largest regional stock exchange in the United States, the Chicago Stock Exchange.

The Chicago metropolitan region generated $651.2 billion in economic output in 2016. In a 2014 study, Chicago ranked 9th among the world's strongest metropolitan areas and 3rd within the United States.