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.

https://www.dfa.ie/irish-embassy/usa/our-services/citizenship/born-outside-ireland/foreign-births-registration-guide/