Patrick and Kathleen Hayes County Cork Ireland

Hi!
I am working on my family tree and am now focusing on my grandmother's family. Her name was Mary K.(Hayes) Calnan. She came over to the USA when she was about 20, from Cork.Her parents were Patrick and Kathleen Hayes.
I have an old letter telling me they were from Cregg North, Glandore, Co. Cork and had 6 or 7 children.
I will start with the census and go from there. All of my family is gone now and there is no one left to get details from here. If anyone might have a bit of info on the,please let me know.
Happy Hunting !
Ellenmarie