Callahan - The surname Callahan is generally accepted to be a variation of the Irish surname Callaghan itself an Anglicized form of the Gaelic Ó Ceallachán 'descendant of Ceallachán'. The name is also sometimes considered to be a diminutive of the name Ceallach, meaning contention or strife. The name Ó Ceallachán was borne by a 10th century king of Munster, from whom many present day bearers of the surname claim descent.[1]
The surname Callahan is fairly common in America and there are families with this name in all parts of every state. John Callahan is the only known member of his family to emigrate and settle in the United States. Although it is quite possible other members of his family preceded or followed him to this country or others with the same name, both here and abroad, are in some way connected, these genealogies do not address this. The genealogies on this site are of those known descendants of John and Mary (Foley) Callahan.
[1] | Patrick Hanks & Flavia Hodges - A Dictonary of Surnames - (Oxford University Press) pp90 |