DeKalb ( dih-KALB) is a city in DeKalb County, Illinois, United States. The population was 40,290 at the 2020 census. The city is named after decorated Franconian-French war hero Johann de Kalb, who died during the American Revolutionary War. Founded in 1856, DeKalb became important in the development and manufacture of barbed wire, especially for agriculture and raising livestock. While agricultural-related industries remain a facet of the city, along with health and services, the city's largest employer in the 21st century is Northern Illinois University, founded in 1895. DeKalb is about 65 miles (105 km) from downtown Chicago.