The Princes of Annaly and Burke's/Debrett's references

If you search specifically for British/Irish genealogical and peerage-style works where a person's pedigree identifies the Annaly Kingdom or Farrell/O'Farrell ancestry as descending from the “Princes of Annaly.” There are several promising lines, but I would distinguish the references I can independently verify from Burke's/Debrett's references that still need exact edition/page confirmation.

References that you can easily substantiate

The Nichols reference is particularly valuable for your purpose because it isn't simply a history of Ireland. It occurs inside the genealogy of an English landed family. Nichols writes of William Farrell, born in Dublin and subsequently connected with an English landed family, that he came from the ancient and honourable Farrell family and was:

“descended from the Princes of Annaly”

and then gives the Farrell arms, crest, supporters and motto.

That's precisely the type of British nobiliary/genealogical usage you were describing.

Burke's and Debrett's

The search results confirm that Annaly.org attributes similar treatment to Burke's Peerage and Debrett's, but at present the searchable web results lead back to Annaly.org rather than giving me scans of the relevant Burke's and Debrett's pages themselves.

So I would presently make the bibliography:

Verified

To locate by exact edition/page

• Burke's Landed Gentry
• Burke's Peerage, Baronetage and Knightage
• Burke's Irish Family Records
• Burke's Genealogical and Heraldic History of the Landed Gentry of Ireland
• Debrett's Peerage and Baronetage
• Debrett's Baronetage / Peerage of the United Kingdom
• Older Irish landed-family pedigrees containing Farrell/O'Farrell maternal descents.

And your idea of searching other peerage biographies is particularly good. We shouldn't search only the O'Farrell entry. A Burke's pedigree for an English or Irish noble family might say, for example, that an ancestor married a daughter of a Farrell “of the ancient Princes of Annaly.” Nichols already demonstrates exactly this phenomenon.

That potentially gives us dozens of independent appearances of the designation scattered throughout British landed-family genealogies.

The evidentiary value is also slightly different from what we've been discussing about the modern Honour. These sources do establish that “Princes of Annaly” was accepted conventional genealogical language in respectable British historical/genealogical literature, rather than a designation recently invented for the modern Honour.

The best verified references I found are:

1. Bernard Burke, Heraldic Illustrations, with Annotations, vol. III (1853). In the arms associated with the Worthington/Farrell connection, Burke writes: “O’Ferrall, Princes of Annaly in Ireland.” This is especially useful because Burke is not merely discussing Irish folklore; he is using the description in a British heraldic-genealogical work while tracing an English landed-family quartering.
2. John Woody Papworth, An Alphabetical Dictionary of Coats of Arms Belonging to Families in Great Britain and Ireland. Under Farrell, Papworth identifies the Connaught family as “descended from the Princes of Annaly,” and connects the line with Farrell of Skeffington Hall, Leicestershire, and Farrell families in Dublin and Cheshire. This is a particularly good example of the phrase entering mainstream British armorial genealogy through descendants outside Longford itself.
3. John O’Hart, Irish Pedigrees; or, The Origin and Stem of the Irish Nation, 5th ed. (1892), vol. I. The entire O’Farrell pedigree is expressly headed “Princes of Annaly.” O’Hart repeats the designation elsewhere when discussing Awly O’Farrell, calling his line the “O’Farrell (Princes of Annaly) pedigree.”
4. O’Hart, The Irish Landed Gentry When Cromwell Came to Ireland. Again, when tracing descendants through Awly O’Farrell, O’Hart explicitly refers readers to the “O’Farrell (Princes of Annaly) pedigree.”
5. British landed-family histories derived from the Farrell–Skeffington line. One published English local history describes William Farrell as originally from Connaught and “descended from the princes of Annaly,” adding that the family had borne those arms from time immemorial. The marriage carried that ancestry into the Skeffington estate in Leicestershire.
6. James P. Farrell, History of the County Longford (1891/1894). This historical work repeatedly identifies the O’Ferrall sept as the “Princes of Annaly” and treats their government as the ruling dynasty of the territory.
7. Later Irish genealogical/armorial literature. The same formulation survived into derivative genealogical works: “O’Ferrall, Princes of Annaly” and “ancient princes of Annaly” appear in armorial and county-history material rather than only in modern clan publications.

There is also an important National Library of Ireland manuscript pedigree, Roger O’Ferrall’s Linea Antiqua, dated 1709. I have confirmed the NLI catalogue record for that 241-page genealogical manuscript, although the catalogue description itself does not provide a searchable “Princes of Annaly” quotation. It would be valuable as an earlier pedigree source if the manuscript can be inspected.

On Burke, therefore, we can now be definite: Burke did not merely imply princely ancestry. Bernard Burke actually printed “O’Ferrall, Princes of Annaly in Ireland.”

On Debrett’s, I am still more cautious. I found modern assertions that Debrett’s recognized the princely origin, but I have not yet obtained a digitized Debrett’s primary page containing the exact phrase. The search results currently point principally to modern Annaly material rather than a scan of Debrett’s itself. So I would presently list Debrett’s as reported/awaiting exact page verification, rather than quote it as though I had the original page in front of me.

The overall evidentiary conclusion is nevertheless quite strong: by the nineteenth century, “Princes of Annaly” was established language in mainstream British heraldic and genealogical literature, including Bernard Burke. It was also used when describing descendants of the O’Farrell line who had entered English landed families—not merely as a local Irish courtesy style.

That is significant for your Annaly analysis because it demonstrates that Annaly itself was conventionally understood as a princely territorial dignity in British nobiliary genealogy long before the modern Westmeath conveyance. What it does not by itself decide is whether that princely characterization followed the later alienable Honour/Seignory; that remains the succession question we have been examining.