The first Catholics in Illinois were French

As Illinois celebrates its bicentennial this year, The Observer will present occasional features from Rockford Diocese history books.

As long as Illinois and the vast territory east and west of the Mississippi was a possession of France and its civil government under the jurisdiction of France, the language, customs and institutions of the Illinois settlements were French, and the priests who labored in these missions were French. They were the Jesuits and the Fathers of the Foreign Missions or Seminary of Quebec.
The Illinois church was under the jurisdiction of the Bishop of Quebec until the year 1784, when, on June 9, by a decree of the Propaganda de Fide of Rome, the newly federated United States became a separate ecclesiastical division, and the Very Rev. John Carroll was appointed Prefect Apostolic. In the year 1810 Illinois came under the jurisdiction of the new Bishop of Bardstown, Ky., and in 1827 of the new Bishop of St. Louis, the Rt. Rev. Joseph Rosati, D.D.
Source: 1924 Complete History Book of the Diocese of Rockford