It is a suffragan diocese of the metropolitan Archdiocese of Chicago. During the 17th century, present day Illinois was part of the French colony of New France. The Diocese of Quebec, which had jurisdiction over the colony, sent numerous French missionaries to the region. It was estimated that 15, to 20, Native American converts and French trappers and settlers throughout the region were tended to by these Jesuit missionaries.
After the British took control of New France in , the Archdiocese of Quebec retained jurisdiction in the Illinois area. However, most of the French Catholics in the area migrated to Louisiana.
In , the new United States claimed sovereignty over the area of Illinois. In , the vicar apostolic, John Carroll , sent his first missionary to Illinois. Pius VI created the Diocese of Baltimore , the first diocese in the United States, to replace the prefecture apostolic in When the Vatican erected the Diocese of Bardstown in Kentucky in , it gained jurisdiction over the Illinois area. The jurisdiction over northern Illinois shifted in to the Diocese of St.
With the creation of the Diocese of Chicago in , northern Illinois was transferred from the Diocese of St. The Rockford area would be part of the Diocese of Chicago, followed by the Archdiocese of Chicago, for the next 64 years. In Elgin, the first Catholic church, St.
Mary's, opened in James, founded in The first parochial school in the city was started in Its territory of 12 counties was taken from the Archdiocese of Chicago. During his tenure, Hoban opened many elementary and high schools in the diocese, modernized charitable institutions , and established a diocesan newspaper. During his tenure as bishop, Boylan was able to reduce the diocese's debt while adding new parishes and schools to meet population growth.
