https://en.wikipedia.org/wiki/Fitzstephen
https://www.libraryireland.com/names/or/o-rioghbhardain.php
https://en.wikipedia.org/wiki/Riordan
This most interesting surname is the Anglicized form of the Gaelic surname “O’Rioghbhardain”, a numerous sept found exclusively in the Province of Munster. The Gaelic name itself is composed of the Gaelic prefix ‘O’, male descendant of, and “Rioghbhardan”, a byname composed of the Gaelic elements “riogh”, royal and “bhard”, a bard, poet.
The surname is also found as Rearden and O’Riordan.
The sept of O’Riordan originated in County Tipperary, and migrated to County Cork at such an early date they can be regarded as belonging to that county, where they are far more numerous than anywhere else. They gave their name to Ballyreardon in East Cork, which indicates that they were influential in this area, where they were followers of the lords of Muskerry. Several County Cork O’Riordans appear as Irish soldiers in the 17th Century.
MacFirbis mentions a family of “O’Riordan”, who were historians of Eile, but little is known of these.
A branch of the O’Riordans, from Derryroe, Cork, settled in Nates in 1753 and became Peers (lords) of France.
Michael Riordan, aged 22 yrs., was an Irish famine immigrant, who left Cork on the ‘Liberty’ for New York on May 21st 1846.
The first recorded spelling of the family name is shown to be that of Domhnall O’ Rioghthardain, which was dated 1658, in the “All Ireland Census”, during the reign of Oliver Cromwell, known as “The Lord Protector”, 1658 – 1659.
Surnames became necessary when governments introduced personal taxation. In England this was known as Poll Tax. Throughout the centuries, surnames in every country have continued to “develop” often leading to astonishing variants of the original spelling.
It seems there is not an active clan organisation for your name, at this time.
However, the revival of interest in Irish culture and heritage over the past 100 years has led to the revival of many Irish Clans. In more recent times, increased access to historical archives online, DNA testing and ease of travel to Ireland has led many individuals to explore their own genealogy and connections to Irish Clans. Some of these have gone on to establish Clan Associations in Ireland, the USA, the UK, Canada, Australia, New Zealand and anywhere that the Irish Diaspora has found itself.
Clans of Ireland Ltd invite those interested in Irish Clans to contact them with a view to explore the possibility of reviving your Irish Clan.