A fascinating source are newspaper advertisements for missing friends and relatives from Ireland. In order to reconnect with someone, ads would be placed with what little information that is known. Cast the net wide in a well known newspaper and see what comes back to you. The Boston Pilot was one of these newspapers.
Boston Pilot ads (1831-1920) have been published and are online. One excellent database is hosted by the New England Historic Genealogical Society: www.americanancestors.org Another database can be found on the Boston College website: infowanted.bc.edu The collection consists of 40,399 records ranging from simple to detailed.
An ad may be placed a decade or later after the immigration occurred. Also, just because the Boston Pilot was a Jesuit publication, don’t assume every ad is placed by a Catholic looking for Catholics. Not all Irish remained with the church. I have found many Protestant converts placing ads or the subject of ads. Don’t assume the Boston Pilot only went to Boston residents. It had a worldwide audience. You will find ads looking for people in almost every place imaginable.
Each database has its strengths and weaknesses. A place search may be what you need, and this can be done by county, parish, town or townland. Perhaps you need only one surname from one county. Make sure the online databases can provide you with your search parameters. If you have doubts, then certainly consult the incredible printed copies which are meticulously indexed in just about every direction possible.
I consult these ads on a regular bases, and often I do find who I am looking for. In these cases typically listed will be the origins in Ireland, when immigrated, where settled, and who is looking for them. By Irish research standards this is incredible.