Hi, I live in Co Kerry. Unfortunately O Sullivan is probably the most common surname in Co Kerry.I have a great granaunt who emigrated to the US named Margaret Sullivan.When I was looking for her before I knew where she had gone ,I was shocked by the amount of Sullivan families in Kerry of which a lot had a Margaret in the family. I was luckily that I knew her parish and parents names . Therefore I found her baptism cert and from there after researching for a year I found her in the US. The Irish state only registered births from the mid 1860's. The only document before that are church baptism certificates. Lots of churches in Kerry now allow you to view these document on - line.But you would have to know the parish of birth and the parents names. The only other existing documents are the applotment books( these only mention the name of the head of each family and a discription and value of the property) . If it helps parents would normally call their first son after the fathers father and the second son after the mother's father. The first daughter was usually called after the fathers mother and the second daughter after the mother's mother.This was the case in 95% of irish families up until the mid 1950,s.In using this method you would have to know of all children within the family who were born starting from the eldest, keeping in mind when a child died young the next born baby of the same gender would inherit the name.Also remember that if a man had four sons ,each of his sons would call their first born male child after the child's paternal grandfather. Therefore a lot of cousins had the same name. The death rate in children under four yrs was very high and people had an average of 10 children. If you do find the names of your Margaret Sullivan's parents or parish or if you know any of her siblings or children with an unusual or rare name it will make it easier . Then I suggest you look at the free site : Irishgeniology.ie : search under church records . Also rootsireland.ie Is a good site if your willing to pay a small fee. The only other way is to join ancestry .com and take a DNA. This helped me with my family tree. It can tell you from a matched DNA with another person what other members DNA share with both you and the match. This can sometimes tell you which side of the family connects you to this person. A lot of matches will have public family trees that can be viewed. You are also allowed to contact members through the ancestry site . I hope this helps some bit and I wish you all the best with your research.Jacqui.