Searching for family information

Hello. I'm hoping to find more information about my family and where they are from. I posted a couple weeks ago asking how I go about finding the next generation in my family tree. I got a response saying I needed to know names and locations to help get more information about them.
So I found names thanks to a 4th cousin I found on ancestry.com. I had asked about my 3x's great grandfather Martin Kelly born about 1833 (I think august). I know he was born in Ireland but I'm not sure where. His parents were Finton and Ellen Kelly.
His wife was Ellen Elizabeth Dunn born January 1830 (possibly 1834). She is the daughter of James and Ellen Kelly. She was born in limerick, hibernian, Ireland.
They married in the United states in 1850. They had a son named martin and a daughter named mary ellen that I know of.
I would love to know birth and death dates of martin and Ellen's parents. Also where they are from exactly and any other information about them, such as other family or their jobs. My 4th cousin said hes been to cork county and found nothing there.
Any help is greatly appreciated, even if it's just telling me where to look. I love doing research and dont mind doing the work myself. I just have no idea where to look or how to find this.