Ó Riaghain
Ó RIAGHAIN, Ó RIAIN—I—O Rian, O'Ryan, Ryan: 'descendant of Riaghan,' or 'Rian'; the name of a Carlow family who were lords of Uí Dróna, the present barony of Idrone, and are now numerous through Leinster; to be distinguished from Ó Maoilriain of Munster and Ó Ruaidhín of Connacht, which are both now incorrectly anglicised O'Ryan or Ryan.
Alphabetical Index to Irish Surnames