Chicago Union Station is a major railroad station that opened in 1925 in Chicago. It is the only remaining intercity rail terminal in Chicago.

The station stands on the west side of the Chicago River between West Adams Street and West Jackson Boulevard, just outside the Chicago Loop. Including approach and storage tracks, it covers about nine and a half city blocks — mostly underground, buried beneath streets and skyscrapers.

Chicago Union Station is the third-busiest rail terminal in the United States, after Grand Central Terminal and Penn Station in New York City. It is Amtrak's overall fourth-busiest station, and the busiest outside of its Northeast Corridor. It handles about 140,000 passengers on an average weekday (130,000 Metra riders and 10,000 Amtrak) and is one of Chicago’s most iconic structures, reflecting the city’s strong architectural heritage and historic achievements. It has Bedford limestone Beaux-Arts facades, massive Corinthian columns, marble floors, and a Great Hall, all highlighted by brass lamps. In 2011, its lighting system was replaced with more energy-efficient light bulbs and motion sensors, reducing the station’s annual carbon emissions by 4 million tons. Custom steel lighting covers were added to top these safety/light towers, helping them blend in with the overall neoclassical style of the station.

Chicago Union Station was designated as one of America's "Great Places" in 2012 by the American Planning Association (APA). The program recognized the station as a "Great Public Space" for promoting social activity and reflecting local culture and history. In celebration of the 2018 Illinois Bicentennial, Union Station was selected as one of the Illinois 200 Great Places by the American Institute of Architects Illinois component (AIA Illinois).