Hi Chris,
Thanks for your message.
Firstly to clarify, Castlegregory is a town, that is located in the parish of Killiny. Co. Kerry. Follow this link to the irishtimes website, where you can see a brief overview of the parish and its townlands:
http://www.irishtimes.com/ancestor/fuses/townlands/index.cfm?fuseaction=TownlandsInCivil&civilparishid=1148&civilparish=Killiney&citycounty=Kerry
You can also use the irishtimes website to get an overview of what Catholic records are available for the Killiny Parish. Perhaps if you can find a birth record for Thomas, you will be able to find the names of his parents. Follow this link:
http://www.irishtimes.com/ancestor/fuses/rcparishmaps/index.cfm?fuseaction=showidrecords&CityCounty=Kerry&parish=Killiny&churchid=660
For Church of Ireland Records check http://ireland.anglican.org/about/42 and http://www.nationalarchives.ie/
You could also do a search for the Fitzgeralds and Smyths in the 1901 and 1911 census records here:
http://www.census.nationalarchives.ie/search/
With regards to the Galway connection:
Do you have any other information on Tom's siblings that you could share? Do you know their names, dates of births, when they may have emigrated? perhaps if you had this information you could search for Tom's sibling in the US Immigration records. A good place to start searching for these is the US National Archives at the following link:
http://www.archives.gov/research/immigration/passenger-arrival.html#film
Perhaps also, as the people you are researching lived in the 20th century, there may be people in the area that remember the name or the family/descendants of the family. Consequently it might be an idea to place a message in a local paper to see if you can make any connections? The two best papers will probably be the Connaught Tribune and The Galway Advertiser. Here are the links for them:
http://www.galwaynews.ie/connachttribune
http://www.advertiser.ie/galway
I hope that this information helps. Remember to post as much information as you can with regard to the people you are researching. The more information you post, the more likely it is that one of our volunteers will be able to advise or assist you. Also include information concerning which sources you may have already used so others may further your search.
Kind regards,
Genealogy Support