Uncle Dave Dooley dreams of locating his Irish Roots. It has become my job to help him realize his dream. Uncle Dave believes his family origins lie in Westmeath, Ireland. But do they really?
Loretto Szucs wrote a nice book, Chicago & Cook County; A Guide to Research. It is a great book that guides a researcher through the vast resources that Chicago has to offer. I looked to his “Ethnic Resources” chapter to learn about the Irish of Chicago. The source of his information comes from an article, “The Irish in Chicago,” written by Kyle J. Betit and Thomas M. Cook.
The Potato Famine of the 1840s was the reason many Irish Catholics left home and arrived in Chicago. According to Mr. Szucs, the Irish settled in three specific locations in Chicago each with it’s own Catholic Parish.
1. The West side between Halsted and the Chicago River from Lake Street south to Harrison (St.Patrick's)
2. The North side from Market Street to Indiana; which is now Grand Avenue. (Holy Name)
3. The Southside along the south branch of the Chicago River. (St. Bridget’s)
A second wave of Irish Catholic immigrants arrived in the 1880s. This group of
immigrants originated from the counties of Mayo and Galway. 
It is this 1880 group of Irish Catholic immigrants that our Dooley ancestors
belonged. The 1900 U.S. Census reports that William Dooley immigrated in the year
1886. Based on what I have learned thus far, if William Dooley arrived in
Chicago in 1886, he may have originated in the counties of Westmeath, Mayo or
Galway. I have my Irish starting point.
Loretto Dennis Szucs, Chicago & Cook Count: A Guide to Research (Salt Lake City: Ancestry, 1996), 265-266.