Local genealogists can often go to great lengths to collect information that is of benefit to a much wider number of researchers. One such person is Tom Cook, a native of Chicago. Over many years he collected a large amount of records of interest to those with Irish ancestry in the Chicago area.
Chicago Irish Families, 1875-1925 is now one of the thousands of Ancestry.com databases. The blurb reads, "this database is a collection of records regarding many of the Irish families who made their home in this city between 1875 and 1925....information provided includes births, marriages, and deaths, often including names of relatives. Taken from a wide variety of sources, including local histories, parish records, local newspapers, and cemetery inscriptions, this can be an extremely helpful database for those researching Irish-American ancestors." The database was expanded in 2012, as reported by Irish Genealogy News.
It seems to have had a previous life as an unpublished manuscript, Chicago's Irish Families 1831-1900, before going live on Ancestry in 2000. Examples of entries can be seen in these extracts of Callahan names (along with some others). Further information that will aid researchers using this database can be found at this link.
Efforts to find out the whereabouts of this manuscript were unsuccessful. Also, it does not seem to be clear as to why records from 1831-1875 were not included on the Ancestry version. Does anyone out there have more information on this interesting resource?