Recorded in a wide range of spellings including Gilhooley, Gilhooly, Gillooly, Gollowly, Gilhouley and Gilluley, this is an ancient Irish surname.It derives from the pre 10th century 'Mac Giolla Ghuala', which translates literally, as 'The son of the follower of (St) Ghuala', an early holy man, believed to have been extant in the 6th century. Most Irish surnames originate from an original chief, and in particular the qualities or personal characteristics with which that chief was associated. The Clan MacGillehowley, in its original spelling, is particularly associated with the counties of Leitrim and Roscommon, and for centuries was rarely found in other parts of Ireland. It is said that a branch or sept of the clan was to be found in County Limerick after the 18th century, but otherwise only in Dublin. The earliest recording of the surname is in the year 1243 in the annals known as 'The Four Masters'. This did not refer to a personal recording, but to the fact that the clan were an offshoot of the O'Mulvey's, although this is doubtful. In the 15th century three priests called MacGillhowley administered to the parish of Kitoghert, County Leitrim, between the years 1460 and 1510. The first hereditary recording in the modern era is probably that of Teig MacGillooly of Granard, County Longford, in 1657.