DuPage County is a county located in the U.S. state of Illinois. Its county seat is the city of Wheaton. DuPage is one of the five collar counties and 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.
The most populous municipality within DuPage County is Naperville. The next largest communities are Wheaton and Downers Grove. A small portion of the City of Chicago is located within the county limits; however, this area is primarily commercial and, as of recent census estimates, has only 230 residents. DuPage County also has a portion of Aurora, which is within Kane, Kendall and Will counties as well.
DuPage County was formed on 9 February 1839 out of Cook County. The county took its name from the DuPage River, which was, in turn, named after a French fur trapper, DuPage. The first written history to address the name, the 1882 History of DuPage County, Illinois, by Rufus Blanchard, relates: