Hi there,
You really need to have some idea of a more precise place of origin in order to start your research. For the moment, there are a number of avenues I would suggest you try lloking:
You can information about the frequency of the name in the mid-19th century and any other variant spellings of the name here: http://www.irishtimes.com/ancestor/surname/ The name is more commonly known as Geraghty here. The exact spelling of names was not always a priority and people were not too bothered how it was written. Sometimes officials wrote the name down and did not know how to spell it, and this is the spelling that is carried down through generations.
Do you know much about their emigration? Dates, the reason why they left, etc? Generally more information was given at the port of arrival rather than the port of departure. If you knew which city they arrived at (e.g. Liverpool), this could be a good place to find more information, and perhaps even find out an exact place of origin. Also check the records in the US. Ellis Island records (www.ellisisland.org) or the Castle Garden records (www.castlegarden.org).
Civil registration records are available from the General Register Office (GRO). These start from 1864 however. You can access the website here: http://www.groireland.ie/research.htm
You could also try checking the land records called the Tithe Applotment Books (1823-38) or the later Griffith's Valuation (1848-64). Griffith's is freely available here: www.askaboutireland.com or here: www.failteromhat.com Failte Romhat has lots of other useful links you could try looking at. Tithe Applotment Books (1823-38). Microfilm copies of the books for all of Ireland are available at the National Archives of Ireland (NAI) http://www.nationalarchives.ie/genealogy1/genealogy-records/tithe-applotment-books-and-the-primary-griffith-valuation/ or the Church of Latter Day Saints (LDS).
Please make sure you link anyone else in your family who is interested in their Irish heritage to our site - and indeed anyone else you know of Irish heritage.
Kind regards,
Sinead Cooney
Genealogist (Ireland XO)
