Catholic Church Records
Sometimes, these can have some really useful information. For example, parish membership lists were occasionally published, showing all the families at a given time, along with names, places of birth, dates, etc. Baptismal entries (infants, normally) and Confirmation entries (usually around age 13) typically give place of birth and parents' names.
Catholic Church records for Boone and Winnebago and several other counties are on microfilm at the Rockford Diocese vault in Rockford. However, no research may be done at the Diocesan level. You must write or visit the parish. Included in this diocese are all the Northern Illinois counties between here and the Mississippi River (Chicago and Joliet Dioceses pick up Cook, Lake, Will, Kendall, Du Page and a few other of the eastern counties.)
All of the Catholic Church records for Cook County, Milwaukee County, the Twin Cities, etc. have been microfilmed by the Mormons at their respective diocesan archives. Rockford, however, is one of a handful of Catholic dioceses that won't allow them to microfilm the old church books. I strongly recommend that you write to the Diocese of Rockford (1234 North Court Street - 61101) and let the Bishop and his staff know that you are in favor of letting the Mormons microfilm the old records. Explain to them how this would benefit everyone -- including their archivists--who would be able to refer requests in the future to the Family History Center and not have to deal with us themselves.