The Roman Catholic Archdiocese of Chicago (Latin: Archidioecesis Chicagiensis) was established as a diocese in 1843 and as an archdiocese in 1880. It serves more than 2.3 million Catholics in Cook and Lake counties in Northeastern Illinois, a geographic area of 1411 square miles. The archdiocese is divided into six vicariates and 31 deaneries. This local church is headed by the Most Rev.