Hi Katherine
I too am looking for a Byrne family. My great great grandmother was Catherine Byrne who could have been your James Byrnes older sister. All I have is that she was born and lived in County Cork and was married at St Mary's, Shandon in 1831. I am guessing she was born around 1811/1812, but could be later. I have no parents names for her. She married Thomas Griffin and had 7 children, all babtised at St. Mary's, Shandon. One son, John, came to New Zealand and married my great grandmother. I have no knowledge of what became of the rest of the family or when Catherine died.
It would be so great if we could find a connection to our families!!
Kate Wright.