I have been researching in the Irish Catholic Parish Records on the National Library of Ireland(NLI) again. For Irish genealogists, this is a breakthrough that most of us never anticipated we would get, being able to research from our homes.
However, in order to take advantage of this wonderful gift that we have been given, you need to know the "Holy Grail" of Irish genealogy, your ancestor's townland or at the very least their county of origin.
I have been lucky in my research, our family lore told me that the Donahues were from Killarney and relentless research has given me the Talents and O'Connells in Queens County( now County Laois). You have to leave no stone unturned in your search for this information. What stones does that involve?
Every birth, baptism (and be sure the write down the godparent's names) death, obituary (check pall-bearers) and marriage (note the witnesses). Not just for your ancestor, for every sibling. Check the people who live around them, especially soon after they arrived from Ireland. People tend to go to areas where they know someone or where people from back home live. The census is your friend in this endeavor.
Check the Boston Pilot for advertisement, friends, and relatives took ads out looking for loved ones. Depending on when your ancestor came, the World War I draft records or the SSI index can provide important information.
Naturalization records can also provide important information but it really depends on which state they naturalized in. Immigration records are potentially helpful as well, though, unless your ancestor has an unusual name, it is hard to tell which one is your ancestor. A name like John Murphy will give you dozens of possibilities
Don't forget to talk to every relative you can locate. You never know what stories have passed down through other branches of the family.
If you can at least narrow it down to the county then you need to try to figure out the date of birth. If your family is anything like mine, the dates will never be obvious. Every census changes the possible birthdate. Just get the info all together and that will be your date range.
Now, without parents names, how do you figure out who the parents actually are? One way is to check the names of the children. While it is not a sure way to get the parents names, many Irish families follow a naming pattern. The first son is named after the father's father and first daughter after the wife's mother. The second son is named after the mother's father and the second daughter is after the father's mother. One side of my family uses this pattern, the other does not so it is a crap shoot but what the heck, it is the best shot you have.
Every record you look at has layers of information, if you can scan it, you will have it all at your fingertips but at the very least write down every single thing. With the parish records, you can print the screenshot and keep it in your files so that you can look at it again any time you need it.
Be prepared to strain your eyes reading the records in the NLI Catholic Parish Records. Some of the records are in Latin and others are in terrible shape and even worse handwriting but even with that, they are worth spending days, weeks, months and even years looking through.