O’Riordan, ó Ríoghbhardáin, ó Ríordáin, A Gaelic surname meaning descendant of Rígbardán, meaning ‘royal poet’. Rígbardán mac Con Coirne, King of Eile who was slain in 1058 at the battle of Sliabh gCrot was an ancestor of the sept. They later moved into Desmond, to west Cork and Muskerry in particular. They were followers of the MacCarthy’s. In 1890 Riordan was numerous in Cork (94 births), it was also to be found in Kerry and Limerick. The estimated number of bearers was 7,123 (including variants). In the United States Reardon is the 2,372 most numerous surname with an estimated 13,750 bearers.
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