Reardon
An Irish surname, usually an Anglicized form of Ó Riordáin / Riordan.
The #2,509 most common surname in the United States (2010 Census) — about 1 in every 21,389 Americans shares it.
Etymology
Reardon is generally treated as an English spelling of the Irish surname Riordan, usually from Ó Riordáin. The Gaelic personal name is commonly explained as containing a descriptive element meaning something like "grey" or "dark-grey," though early sources differ in details. The surname therefore began as a family name connected to an ancestor's byname rather than to an occupation or place.
History
19th-century surname books regularly link Reardon directly with Riordan and list several spellings such as O'Riordan, Reardan, and Reardon. It is an established Irish surname that spread into English-speaking records through Anglicization and migration, especially in the 19th and 20th centuries. Some older authors treated the form as one of several variants under the same Irish family name.
Origin
Regions
Variant spellings
Fun fact
Older reference books often grouped Reardon, Riordan, and O'Riordan together as the same surname family, just in different spellings.
From the historical record
“Rhys, Celt. Brit., ed. 1908, p. 313. REARDON = Riordan, q.v. REASBECK, a var. of Ralsbeck, q.v. REASON I Rea's Son : v. Rea. 2 a var, of fiayson and Rasen, q.v. REAVY 1 (Celt:) Grey [Ir. and Gael, riabhach REAY / (bh as v, and sometimes mute] But the Caithness place-name Keay (13th cent. Ra, i6th cent. Ray) is app. the”
— Surnames of the United Kingdom: a concise etymological dictionary (2 vols in 1)