I have a Ellen Riordan born in Cork probably in the mid 1850's. She had a brother Timothy and came to New York City probably in the early 1880's. Their parents were Margaret Sheehan and Daniel Riordan who married on April 28,1850 at St. Finnbars in Cork and lived for a time on Nicholas Street in Cork. I am planning to research the Irish records on my Riordans of Cork - hopefully this year.
By the way, Ellen, after marrying Peter Peterson had five children born in NYC, the last one was a Honora born in 1894 and died in 1898. The others were Margaret, John, Cornelius, and Catherine.
I hope somehow this helps you in your search.