Coordinates: 41°50′N 88°05′W / 41.833°N 88.083°W / 41.833; -88.083

DuPage County is a county located in the U.S. state of Illinois. Its county seat is the city of Wheaton. This county is part of the Chicago metropolitan area. According to the 2010 census, it has a population of 916,924, which is an increase of 1.4% from 904,161 in 2000. It is the second most populous county in Illinois after Cook County, which borders it to the north and east; the two counties account for half of the state's population. The county is divided into nine different townships: Addison, Bloomingdale, Downers Grove, Lisle, Milton, Naperville, Wayne, Winfield and York. The majority of DuPage County is in the 630 and 331 area codes. However, the areas of the county that are in the city of Chicago are in area code 773, primarily part of O'Hare International Airport.

Long known as one of the nation's wealthiest counties, DuPage County has transformed itself from a primarily agricultural economy to one rich in many different types of commerce. Today, DuPage County has the highest per capita income in the state. DuPage County's per capita income is also the highest in the Midwest. Nineteen of the county's towns have average household incomes of over $100,000.

Illinois (ⁱ/ˌɪlɨˈnɔɪ/ IL-i-NOY) is the 25th most extensive and the 5th most populous of the 50 United States, and is often noted as a microcosm of the entire country. With Chicago in the northeast, small industrial cities and great agricultural productivity in central and northern Illinois, and natural resources like coal, timber, and petroleum in the south, Illinois has a broad economic base. Illinois is a major transportation hub. The Port of Chicago connects the state to other global ports from the Great Lakes, via the Saint Lawrence Seaway, to the Atlantic Ocean; as well as the Great Lakes to the Mississippi River, via the Illinois River. For decades, O'Hare International Airport has ranked as one of the world's busiest airports. Illinois has long had a reputation as a bellwether both in social and cultural terms and politics.

Although the state's largest population centers today are in northern Illinois, originally the state's population grew from south to north, with settlers arriving from Kentucky in the 1810s. In 1818, Illinois achieved statehood. Chicago was founded in the 1830s on the banks of the Chicago River, one of the few natural harbors on southern Lake Michigan. Railroads and John Deere's invention of the self-scouring steel plow turned Illinois' rich prairie into some of the world's most productive and valuable farmlands, attracting immigrant farmers from Germany and Sweden. By 1900, the growth of industrial jobs in the northern cities and coal mining in the central and southern areas attracted immigrants from Eastern and Southern Europe. Illinois was an important manufacturing center during both world wars. The Great Migration established a large community of African Americans in Chicago that created the city's famous jazz and blues cultures.