O'Reilly
family name
O'Reilly (Irish: Ó Raghallaigh) is a common Irish surname. The O'Reillys were historically the kings of East Bréifne in what is today County Cavan. The clan were part of the Connachta's Uí Briúin Bréifne kindred and were closely related to the Ó Ruairc (O'Rourkes) of West Bréifne. O'Reilly is ranked tenth in the top twenty list of most common Irish surnames. It is also the patronymic form of the Irish name Reilly (Irish: Raghallach).
Naming conventions
Overview
Usually anglicised as Reilly, O'Reilly or Riley, the original form of the name, Ó Raghallaigh, denotes "descendant of Raghallach".
The Ó Raghallaigh family were part of the Connachta, with the eponymous Raghallach said to have died at the Battle of Clontarf in 1014.
The name is common and widespread throughout Ireland, ranked 11th most common in 1890 and in 1997.
A self-proclaimed and disputed O'Reilly Clan Chieftain to this day is at odds with the O'Rourke Clan Chieftain because he contests the recognised O'Rourke claim on the title Prince of Breifne. This was settled in 1994 when the Chief Herald of Ireland made the O'Rourke Chief the Prince of Breifne, but the Office of the Chief Herald stopped granting courtesy titles to Gaelic Chiefs in 2003 (see O'Rourke).
“O'Reilly” enters the record as family name. Crown Archives preserves that source wording while asking what O'Reilly, family and name can confirm, complicate or overturn.
Why this record matters
“O'Reilly” is worth following because a concise public description often conceals a longer documentary argument. Here, O'Reilly, family and name provides the most credible route into that argument.
The citation trail is more important than the brevity of the summary: it shows where individual claims can be examined in context. The source revision retrieved here is dated May 1, 2026. The linked authority identifier is Q21482671. None of the 0 selected statements returned an explicit reference. The first chronological checks are 1014, 1890, 1997 and 1994.
Overview language is designed for orientation and should not be treated as a substitute for the evidence cited beneath it. The source lead contains qualifying language; that uncertainty should survive quotation, summary and reuse. Authority statements aid reconciliation but still require their own references, qualifiers and ranks to be checked.
How to read it
Use the entry as an orientation point, then follow its citations and revision history. Names, dates and institutional relationships should be checked against the original record.
- Subject orientation
- Search vocabulary
- Locating named sources
The closest primary source, responsible institution and strongest cited specialist reference.
Three-step research path
- Establish the record: confirm the title “O'Reilly”, its source revision and the description used here.
- Expand the search: follow O'Reilly primary sources, O'Reilly archive and O'Reilly research across catalogues and specialist indexes.
- Test the account: compare the strongest cited source with the responsible institution’s current record and note any disagreement.
Questions for further research
- Which source most directly establishes the central claim about “O'Reilly”?
- Which institution is responsible for the underlying evidence?
- What terminology or title could unlock a more precise catalogue search?
Search terms from this dossier
This entry incorporates text from “O'Reilly” on English Wikipedia. Contributors are listed in the page history. Text is available under the Creative Commons Attribution-ShareAlike 4.0 License. Selected authority identifiers and statements are retrieved from Wikidata under CC0; their references and qualifiers remain part of the verification path.