The Roman Catholic Diocese of Belleville is an ecclesiastical territory or diocese of the Roman Catholic Church in the southern Illinois region of the United States. It comprises the southern counties of the state of Illinois and is administered from the City of Belleville. The See city for the diocese is Belleville. It is a suffragan see of the Archdiocese of Chicago. The cathedral parish for the diocese is the Cathedral of Saint Peter. Its current bishop is Edward Braxton.