MacGowan (or Magowan) is the phonetic anglicisation of the Irish Mac Gabhainn and the Scottish Mac Gobhainn, both meaning "son of the smith". In Ireland the surname originated in central Co. Cavan, in what was once the ancient kingdom of Breffny, where the MacGowans were among the most powerful families. However, in Cavan itself a large majority translated their surname and became Smiths (see also the entry for that name). Outside Cavan, in the adjoining counties of Leitrim, Donegal, Sligo and Monaghan, MacGowan was the most popular English form, and the surname is most numerous in those counties today, with the largest number in Co. Donegal. There, a family of MacGowans held Church lands in the parish of Inishmacsaint. Because of their prominence, a separate Donegal family based near Raphoe, the Mac Dhubhain (from a diminutive of dubh, "black") also anglicised their name as MacGowan, adding to the numbers bearing the name in that county.
Smith is a surname famous for being ordinary; it is the most common name in England, Scotland and Wales, and in Ulster, while it is the fifth most common in Ireland as a whole. Antrim and Cavan are the areas in which it is most numerous. Its English origin, designating an armourer, smith or farrier, and many bearing the name, in Ulster especially, will be of English stock. The Scottish originals anglicised as Smith are Mac Gobha and Mac Gobhainn, both meaning "son of the smith". These were also anglicised phonetically as (Mac)Gow and (Mac)Gowan. At least two major families of the name are recorded, branches of the Clan Donald and the Clan MacPherson. The principal Irish name is Mac Gabhainn, also "son of the smith", and is strongly rooted in Co. Cavan, where the Mac Gabhainn were one of the most powerful families. The vast majority of the family in Cavan anglicised their name to Smith. Among less prominent families adopting Smith were the O Gabhainn ("O'Gowan") of Drummully in Fermanagh and of Co. Down, and the Mac In Gabhand of Ballymagowan in Co. Tyrone.