what county is naperville
County Government. Naperville is situated in two Illinois counties. The portion north of 87th Street is in DuPage County; the portion south of 87th Street is in Will County. Also listed are phone numbers for the respective health departments of each county.
DuPage County is a county located in the U.S. state of Illinois. As of the 2010 census, the population was 916,924, making it the second-most populous county in Illinois. Its county seat is Wheaton. Dupage County is one of the collar counties of the Chicago-Naperville-Elgin, IL-IN-WI Metropolitan Statistical Area. 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.