For records prior to 1915, you can try the LDS FHL. They have filmed birth, marriage and death records of many Chicago parishes and these can be invaluable. Going through these records, I found ancestors no one ever mentioned, children who died as infants and marriages unknown to other family members. For records after 1915, or if the records of the church were not filmed by the FHL, you will need to go through the Archdiocese. If you live in the Chicago area, Julie Satzik, Asst. Research Archivist at the Archdiocese Archives and Records Center, will be at the PGSA on Milwaukee Ave., Nov. 12 at 2 PM. She will speak about "what kinds of records are available at the Archdiocese, what kind of access to expect and the protocol for obtaining records." The St. John the Baptist Church you mention, is it located at 91st & Burley in South Chicago?