The Diocese of Peoria is a Latin Church ecclesiastical territory, or diocese, of the Catholic Church in the north central region of Illinois in the United States. It is a suffragan diocese within the ecclesiastical province of the metropolitan Archdiocese of Chicago.

The Archdiocese of Chicago is a Latin Church ecclesiastical jurisdiction, an archdiocese of the Catholic Church located in Northeastern Illinois, in the United States. It was established as a diocese in 1843 and elevated to an archdiocese in 1880. It serves the more than 2 million Catholics in Cook and Lake counties in the state of Illinois, an area of 1,411 square miles (3,650 km2). The archdiocese is divided into six vicariates and 31 deaneries.