Dillon is an Irish surname of Breton origin, descending from a cadet branch of Viscomte de Leon in Northern Brittany. It first appeared in Ireland with the arrival of Sir Henry de Leon, in the service of Prince John in 1185. Sir Henry married Maud de Courcy, daughter of Sir John de Courcy and Affrica Guðrøðardóttir. Awarded large tracts of land by in Meath and Westmeath, one of the Dillons’ first Mott & Baileys can still be found at Dunnamona before the establishment of stone structures such as Portlick Castle.
The name evolved into the Irish-language "Diolun"/English-language "Dillon" (not to be confused with the Welsh given name Dylan). It is particularly common in the Meath and Westmeath counties of Ireland where the Dillons were granted vast areas of land. The name is widespread throughout Ireland. The Dillon family later became the Barons Clonbrock and Earls of Roscommon. The family in Ireland was honoured with six compositions (music & poetry) composed by Turlough Carolan: Tiarna Duilleain – Lord Dillon; Róis Duilleain – Lady Rose Dillon jig; Gearalt Duilleain – Gerald Dillon; Fainní Duilleain – Fanny Dillon; Comhairleoir Duilleain – Coun. Dillon; Lúcás Ó Duilleain – Luke Dillon.[citation needed].
