You can now browse Archdiocese of Chicago Catholic church records online for free at FamilySearch and because the Archdiocese includes nearby towns, you will also find records for places like Oak Park, Evanston, and Cicero.
To access the images, you'll need to log into FamilySearch but if you don't already have an account, no worries. It's quick and easy to sign up and it's free. To find the images, go to FamilySearch, click on "US, Canada, and Mexico" under "Browse by Location," and scroll down to "Illinois, Chicago, Catholic Church Records, 1833-1925."
These records were digitized from Family History Library microfilm and even though the date in the title goes to 1925, you'll find that the records for most parishes end with 1915. That was the cutoff year when the records were filmed.
So, here are some tips for accessing the records.
1) Many of the books have index pages in the front.
2) If you're not sure which parish to search, locate the family's address in a city directory or on another record, a birth certificate, for example. Then use that address with the search tool at ChicagoAncestors.org to find out which parishes were close to the address.
3) If you're looking for a marriage register entry, find a copy of the marriage license first. Many will list the parish name. If the record doesn't, find the priest in a city directory to see where he was serving, or if it's an early marriage, try searching my priest/parish database for ideas.
4) It's helpful to narrow parishes by ethnicity. I usually use the list at POINTers in Person for that purpose.
Eventually, these records will be indexed, but in the meantime, happy searching.