Chicago is the largest city in the U.S. state of Illinois and the Midwestern United States, as well as the third-most populous city in the United States with more than 2.8 million residents. Adjacent to Lake Michigan, the Chicago metropolitan area (commonly referred to as Chicagoland) has a population of more than 9.5 million people in three U.S. states, Illinois, Wisconsin and Indiana, and was the third largest U.S. metropolitan area in 2000. One of the largest cities in North America, Chicago is among the world's twenty-five largest urban areas by population, and rated an alpha world city by the World Cities Study Group at Loughborough University.

Chicago incorporated as a city in 1837 after being founded in 1833 near a portage between the Great Lakes and the Mississippi River watershed. The city soon became a major transportation hub in North America and the transportation, financial and industrial center of the Midwest. Today the city's attractions bring 44.2 million visitors annually. O'Hare International is the second busiest airport in the world. The city has a notable and famous political culture, is a stronghold of the Democratic Party, and has been home to numerous influential politicians, including the first African-American President of the United States, Barack Obama. Chicago has also been chosen as one of the final 4 candidates to host the 2016 Summer Olympics.

Chicago is located in northeastern Illinois at the southwestern tip of Lake Michigan. It sits on the continental divide at the site of the Chicago Portage, connecting the Mississippi River and the Great Lakes watersheds. The city lies beside Lake Michigan, and two rivers — the Chicago River in downtown and the Calumet River in the industrial far South Side — flow entirely or partially through Chicago. The Chicago Sanitary and Ship Canal connects the Chicago River with the Des Plaines River, which runs to the west of the city. Chicago's history and economy are closely tied to its proximity to Lake Michigan. While the Chicago River historically handled much of the region's waterborne cargo, today's huge lake freighters use the city's far south Lake Calumet Harbor. The Lake also moderates Chicago's climate, making it warmer in the winter and cooler in the summer.

When Chicago was founded in the 1830s, most of the early building began around the mouth of the Chicago River, as can be seen on a map of the city's original 58 blocks. The overall grade of the city's central, built-up areas, is relatively consistent with the natural flatness of its overall natural geography, generally exhibiting only slight differentiation otherwise. The average land elevation is 579 feet (176 m) above sea level. The lowest points are along the lake shore at 577 feet (176 m), while the highest point at 735 feet (224 m) is a landfill located in the Hegewisch community area on the city's far south side.

Lake Shore Drive runs adjacent to a large portion of Chicago's lakefront. Parks along the lakeshore include Lincoln Park, Grant Park, Burnham Park and Jackson Park; 29 public beaches are found all along the shore. Near downtown, landfills extend into the Lake, providing space for the Jardine Water Purification Plant, Navy Pier, Northerly Island and the Museum Campus, Soldier Field, and large portions of the McCormick Place Convention Center. Most of the city's high-rise commercial and residential buildings can be found within a few blocks of the Lake.
Chicago Harbor Lighthouse

Chicagoland is an informal name for the Chicago metro area, used primarily by copywriters, advertising agencies, and traffic reporters. There is no precise definition for the term "Chicagoland," but it generally means "around Chicago" or relatively local. The Chicago Tribune, which coined the term, includes the city of Chicago, the rest of Cook County, eight nearby Illinois counties; Lake, McHenry, DuPage, Kane, Kendall, Grundy, Will and Kankakee, and three counties in Indiana; Lake, Porter, and LaPorte. The Illinois Department of Tourism defines Chicagoland as Cook County without the city of Chicago, and only Lake, DuPage, Kane and Will counties. The Chicagoland Chamber of Commerce defines it as all of Cook, and DuPage, Kane, Lake, McHenry and Will counties.

The city lies within the humid continental climate zone (Koppen Dfa), and experiences four distinct seasons. Summers are warm & humid with average high temperatures of 80-84°F (27-29°C) and lows of 61-65 °F (16-19°C). Winters are cold, snowy and windy with temperatures below freezing. Spring and Fall are mild with low humidity. According to the National Weather Service, Chicago’s highest official temperature reading of 107 °F (42 °C) was recorded on June 1, 1934. The lowest temperature of −27 °F (−33 °C) was recorded on January 20, 1985. Along with long, hot dry spells in the summer, Chicago can suffer extreme winter cold spells. In the entire month of January 1977, the temperature did not rise above 31 °F (-0.5 °C). The average temperature that month was around 10 °F (-12 °C).

Chicago’s yearly precipitation averages about 34 inches (860 millimeters). Summer is typically the rainiest season, with short-lived rainfall and thunderstorms more common than prolonged rainy periods. Winter precipitation tends to be more snow than rain. Chicago's snowiest winter on record was that of 1978–79, with 89.7 inches (228 cm) of snow in total. The winter of 2007-08, with more than 61 inches (155 cm) of snow, was the snowiest in nearly three decades. Average winter snowfall is around 38 inches (96.52 cm). The highest one-day snowfall total in Chicago history was 18.3 inches (46.5 cm) on Jan. 3, 1999. Chicago’s highest one-day rainfall total was 6.63 inches (168.4 mm) on September 13, 2008. The previous record of 6.49 inches (164 mm) had been set on August 14, 1987.

The outcome of the Great Chicago Fire led to the largest building boom in the history of the nation. Perhaps the most outstanding of these events was the relocation of many of the nation's most prominent architects to the city from New England for construction of the 1893 World Columbian Exposition.

In 1885, the first steel-framed high-rise building rose in Chicago ushering in the skyscraper era. Today, Chicago's skyline is among the world's tallest. Downtown's historic buildings include the Chicago Board of Trade Building in the Loop, with others along the lakefront and the Chicago River. Once first on the list of largest buildings in the world and still listed twentieth, the Merchandise Mart stands near the junction of the north and south river branches. Presently the three tallest in the city are the Sears Tower, the Aon Center (previously the Standard Oil Building), and the John Hancock Center. The city's architecture includes lakefront high-rise residential towers, low-rise structures, and single-family homes. Industrialized areas such as the Indiana border, south of Midway Airport, and the banks of the Chicago Sanitary and Ship Canal are clustered.

Future skyline plans entail the supertall Waterview Tower, Chicago Spire, and Trump International Hotel and Tower. The 60602 zip code was named by Forbes as the hottest zip code in the country with upscale buildings such as The Heritage at Millennium Park (130 N. Garland) leading the way for other buildings such at Waterview Tower, The Legacy and Momo. Other new skyscraper construction may be found directly south (South Loop) and north (River North) of the Loop.

Multiple kinds and scales of houses, townhouses, condominiums and apartment buildings can be found in Chicago. Large swaths of Chicago's residential areas away from the lake in the so-called "bungalow belt" are characterized by bungalows built from the early 20th century through the end of World War II. Chicago is also a prominent center of the Polish Cathedral style of church architecture.

The city's waterfront allure and nightlife has attracted residents and tourists alike. Over one-third of the city population is concentrated in the lakefront neighborhoods (from Rogers Park in the north to Hyde Park in the south). The North Side has a large gay and lesbian community. Two North Side neighborhoods in particular, Lakeview and the Andersonville area of the Edgewater neighborhood, are home to many LGBT businesses and organizations. The area adjacent to the North Side intersection of Halsted and Belmont is a gay neighborhood known as "Boystown". The city has many upscale dining establishments as well as many ethnic restaurant districts. These include the Mexican villages such as Pilsen on 18th street and "La Villita" on 26th street, "Greektown" on South Halsted, "Little Italy" on Taylor Street, just west of Halsted, "Chinatown" on the near South Side, "Little Seoul" on and around Lawrence Avenue, a cluster of Vietnamese restaurants on Argyle Street and South Asian (Indian/Pakistani) on Devon Avenue.

Chicago attracted a combined 44.2 million people in 2006 from around the nation and abroad. Upscale shopping along the Magnificent Mile, thousands of restaurants, as well as Chicago's eminent architecture, continue to draw tourists. The city is the United States' third-largest convention destination. Most conventions are held at McCormick Place, just south of Soldier Field. The historic Chicago Cultural Center (1897), originally serving as the Chicago Public Library, now houses the city's Visitor Information Center, galleries, and exhibit halls. The ceiling of Preston Bradley Hall includes a 38-foot (11 m) Tiffany glass dome. Millennium Park, initially slated to be unveiled at the turn of the 21st century, and delayed for several years, sits on a deck built over a portion of the former Illinois Central rail yard. The park includes the reflective Cloud Gate sculpture (known locally as "The Bean"). A Millennium Park restaurant outdoor transforms into an ice rink in the winter. Two tall glass sculptures make up the Crown Fountain. The fountain's two towers display visual effects from LED images of Chicagoans' faces, with water spouting from their lips. Frank Gehry's detailed stainless steel band shell Pritzker Pavilion, hosts the classical Grant Park Music Festival concert series. Behind the pavilion's stage is the Harris Theater for Music and Dance, an indoor venue for mid-sized performing arts companies, including Chicago Opera Theater and Music of the Baroque.

In 1998, the city officially opened the Museum Campus, a 10-acre (4-ha) lakefront park surrounding three of the city's main museums: the Adler Planetarium, the Field Museum of Natural History, and the Shedd Aquarium. The Museum Campus joins the southern section of Grant Park which includes the renowned Art Institute of Chicago. Buckingham Fountain anchors the downtown park along the lakefront. The Oriental Institute, part of the University of Chicago, has an extensive collection of ancient Egyptian and Near Eastern archaeological artifacts. Other museums and galleries in Chicago are the Chicago History Museum, DuSable Museum of African-American History, Museum of Contemporary Art, the Peggy Notebaert Nature Museum, the Polish Museum of America, Museum of Broadcast Communications and the Museum of Science and Industry.