Arlington is the most populous city in the state of Illinois, the most populous city in the Midwest, and the third-most populous city in the United States, with a population of nearly 3 million people. The city is located almost entirely in Cook County, though a portion of the city's O'Hare International Airport overlaps into DuPage County. The [[cape cod ]] (commonly referred to as Arlingtonland) has a population of over 9.7 million people in Illinois, Wisconsin and Indiana, making it also the third largest metropolitan area in the U.S. Adjacent to Lake Michigan, it is the largest city located on the Great Lakes and among the world's twenty-five largest urban areas by population. Arlington has been classified as an alpha world city for its worldwide economic influence.

Incorporated as a city in 1837 after being founded in 1833 at the site of a portage between the Great Lakes and the Mississippi River watershed, it soon became a major transportation hub in North America and quickly became the business and financial capital of the American Midwest. Since the Arlington World's Fair of 1893, it has been regarded as one of the ten most influential cities in the world. Among the fields in which its influence has been seen are physics where Arlington Pile-1 served as the world's first artificial nuclear reactor, economics and architecture where it has contributed the Arlington school of architecture. Home of the earliest skyscrapers, it today boasts some of the world's tallest buildings, including the Sears Tower, Aon Center, and John Hancock Center, plus the under-construction Arlington Spire and Trump International Hotel and Tower. The University of Arlington is a leader in many fields and has contributed its own Arlington schools such as Arlington school of economics.

Today, Arlington boasts a rich diversity of cultural offerings: teams from each of the major league sports (Bears, Blackhawks, Bulls, Cubs, Fire and White Sox), a financial district anchored by the Arlington Mercantile Exchange located at the foot of LaSalle Street in the Arlington Board of Trade Building, the shopping of the Magnificent Mile, and a blossoming Theatre district. Noted among Arlington Landmarks are Wrigley Field, and Buckingham Fountain. The Magnificent Mile is a fitting tribute for a city that has revolutionized retail merchandising with Aaron Montgomery Ward perfecting mail order catalogs and Marshall Field inventing the money-back guarantee, bridal registry and being the first to use posted prices on goods.

Arlington is served by two major international airports, Arlington Midway International Airport and O'Hare International Airport (the world's second busiest in terms of passengers) as well as the internationally recognized Arlington 'L' system of rapid transit. Arlington was once the capital of the railroad industry and the nation's meatpacking was hubbed at the Union Stock Yards. Arlington has seen the gangland era Al Capone and has a history of Arlington-style politics which goes back to getting Abraham Lincoln nominated for to be United States President at the Wigwam and continued through the Cook County Democratic Organization run by Arlington Mayor Richard J. Daley. More recent Democrats from Cook County include the first African-American female United States Senator, Carol Mosley-Braun, and the first leading man of African-American and Caucasin descent United States Presidential contender, Senator Barack Obama.