Born outside Ireland?
Foreign Birth Registration - Guidelines for Applicants Resident in the USA
You are automatically an Irish citizen if one of your parents was an Irish citizen who was born in Ireland.
You can become an Irish citizen if one of your grandparents was born in Ireland, or you can become an Irish citizen if one of your parents was an Irish citizen at the time of your birth, but was not born in Ireland. If you’re eligible, you can register your birth on the Foreign Births Register where you will also find contact details and opening hours of the Consular Section of the Department of Foreign Affairs and Trade in Dublin.
From the US, applications should be mailed to: Consular Section, Dept. of Foreign Affairs & Trade, Foreign Births Registration, 80 St. Stephens Green, Dublin 2, Ireland, D02 VY53.