The family surname Whelan ( /ˈhwiːlən/) is an anglicisation of the Irish surname, Ó Faoláin. The surname originates from the Middle Irish 'Úa Faeláin' (plural, 'Uí Faeláin') the name of the 10th to 11th century ruling dynasty of the Déisi, a population group inhabiting the area of the modern county of Waterford and south county Tipperary in the early medieval period.

The word "faolán" is derived from the Old Irish word "faelán" meaning a small wolf; '-án' being of the diminutive suffix in Irish. "Ó" (anglicised as "O’") derives from the Old Irish "úa", meaning "grandson", or more figuratively "patrilineal descendent". The patronym that follows is always in the genative case, in accordance with Irish grammatical rules, and is normally marked by an "i" following the final vowel. Therefore, the name Faelán, becomes "Úa Faeláin" as a patronym in Middle Irish, from which is derived "Ó Faoláin" in Modern Irish, of which in turn "Whelan", "Phelan", "O'Phelan" etc. are anglicisations.

According to the legendary history of Ireland, about 300 A.D., the Déisi settled on the site of Dungarvan, County Waterford. In the 12th and 13th centuries, during the early Anglo-Norman period, records of a political nature relating to the Déisi and the descendants of the Uí Faeláin dynastic group decline.

The Faelán referred to is Faelán mac Cormac, who is recorded in the Annals of Inishfallen as having succeeded his father as king of the Déisi in 966. The first person referred to as "úa Faeláin" is his grandson Mothla mac Domnall, or Mothla úa Faeláin, who was king of the Déisi until his death at the Battle of Clontarf in 1014, and whose head is recorded in the Annals of Ulster as having been interred with Brian Ború in Armagh. During this period however, Irish patronyms had not yet petrified into surnames proper.

According to the Annals of the Four Masters:

The Age of Christ, 1170. M1170.11 Robert Fitz Stephen and Richard, son of Gilbert, i.e. Earl Strongbow, came from England into Ireland with a numerous force, and many knights and archers, in the army of Mac Murchadha, to contest Leinster for him, and to disturb the Irish of Ireland in general; and Mac Murchadha gave his daughter to the Earl Strongbow for coming into his army. They took Loch Garman, and entered Port-Lairge by force; and they took Gillemaire, the officer of the fortress, and Ua Faelain, lord of the Deisi, and his son, and they killed seven hundred persons there.

By the beginning of the thirteenth century, most of the territory of the Déisi was adsorbed into the Anglo-Norman colony. The surname 'Whelan' remains common in Co. Waterford and in the adjoining part of Co. Kilkenny, particularly in the barony of Iverk.

The earliest anglicised forms of the Ó Faoláin name were Felan, Faelan, Hyland, with many other similar variants, including Whelan and Phelan in Cos Waterford and Kilkenny. Whelan and Whalen are the most prevalent forms in modern times, and combined are placed seventy-ninth in the list of the hundred most common surnames in Ireland. With Phelan added, the name takes forty-fourth place.

Read more about Whelan:  Notable Whelans