genealogies of the families
Click HERE for a Short History of the O'Reilly Name.
O'Reilly, in Irish O Raghailligh, i.e. descendant of Raghallach, was until recently much more commonly found without the prefix 'O'.
Reilly and O'Reilly constitute one of the most numerous names in Ireland, being among the first dozen in the list. The bulk of these come from Cavan and adjoining counties, the area to which they belong by origin, for they were for centuries the most powerful sept in Breffny, their head being chief of Breffny-O'Reilly and for a long time in the middle ages his influence extended well into Meath and Westmeath.
At the present time we find them very numerous still in Breffny, heading as they do the county list both in Cavan and Longford. In 1878 O'Reilly landlords possessed over 30,000 acres.
Five O'Reillys have held the Primacy as Archbishop of Armagh, notably Edmund O'Reilly (1606-1669) and Hugh O'Reilly (1580-1653); five were Bishops of Kilmore, two of Clogher and one of Derry; and another famous churchman was Edmund Joseph O'Reilly, S.J. (1811-1878). Edward O'Reilly (d. 1829) compiled a pioneer Irish-English Dictionary in 1817.
In the field of patriotic endeavour we have John Boyle O'Reilly (1844-1890) the Fenian; Myles O'Reilly M.P. (1825-1880), who commanded the Irish Brigade in the Papal service; and Philip MacHugh O'Reilly (d. 1657), who, having been largely responsible for organizing the rising of 1641 in his own county of Cavan, fought under Owen Roe O'Neill and died in exile. In King James 11's Irish army Col.
Edmund O'Reilly's regiment of infantry included thirty-three officers and Col. Mahon's regiment sixteen officers called Reilly or O'Reilly.
Many of these became Wild Geese. Count Don Alexander O'Reilly (d. 1797), after a distinguished military career in the French, Austrian and Spanish service ended his days as Governor of Louisiana in America.
A good deal of unreliable material is to be found in print on the subject of the O'Reillys. It is therefore advisable to mention that an authoritative article on them appeared in the Irish Ecclesiastical Record Vol. 45-1935, Part 2, from the pen of Father Paul Walsh. In it that famous and almost legendary seventeenth century figure "Myles the Slasher" finds a correct place.
O'Reilly is occasionally found as a synonym of O'Rahilly, but this is merely an example of careless registration since O'Rahilly, which is O' Raithile in Irish, has no connection with Breffny. It is true that the sept originated in Ulster but they have so long been associated with Co. Kerry and they must be regarded as Munstermen, especially as Egan O'Rahilly (1670-1726), greatest of Munster poets - by many regarded as greatest of all Gaelic poets - was of a family long established near Killarney.
Source: Irish Families by Edward MacLysaght MA, D Litt, MRIA - Irish Academic Press 1991
See also: http://www.libraryireland.com/articles/OReillysDuffysHibernian/index.php