Brennan
A common Irish surname, probably meaning a descendant of a person named Brennan or Branan.
The #701 most common surname in the United States (2010 Census) — about 1 in every 6,270 Americans shares it.
Etymology
Brennan is an Irish surname with several closely related Gaelic forms behind it. Historical surname writers connect it especially with Gaelic names such as Ó Brannáin and Mac Brannáin, and with related forms like Branan/Brannan; the core element is likely a personal name rather than a common noun. The exact original meaning of that personal name is not entirely certain, but the surname is firmly Irish in origin.
History
Lower explicitly calls Brennan “undoubtedly Irish,” and Irish surname scholarship places it among older Gaelic family names that later spread widely in Ireland and, through emigration, abroad. It became especially common in parts of Ireland and is now well established in the United States as well. Because several related spellings and Gaelic source-forms overlap, older sources sometimes differ on the exact derivation.
Origin
Regions
Variant spellings
Fun fact
In 19th-century Irish surname studies, Brennan is often grouped with a cluster of very similar names, which is one reason older books give slightly different explanations for it.
From the historical record
“Avriters, to whom the church is dedicated. BRENNAN.* The name is undoubtedly Irish. See Mac Brcnnan in this supple- ment. BRENTON. Probably the same as Brintou. BRE SSINGII A J\ r. A parish in N orfolk . BREST. The well-lcnown town and ar- senal in Brittany.”
— Patronymica Britannica: a dictionary of the family names of the United Kingdom