The surname Monaghan is an anglicization of the Irish surname O'Manacháin //. The Irish translation for this name is descendent of Manacháin, which ultimately translates to "Monk". Other variations include Monahan and Monachan.
Essentially, sometime before the 16th century, the Connacht family derived the name Monahan from the infamous warrior Manacháin mentioned by the Four Masters at the year 866. The O'Manacháin clan were chiefs of Ui Briuin na Sionna in the barony of Ballintober, Co. Roscommon, until the year 1249 when they were ousted by the O'Beirnes.
Although they share the same spelling, the surname Monaghan is not related to County Monaghan, Ireland, who name is derived from the Irish Muineachán. Muineachán (Muinechán, Mhuineachain) means "a place abounding in little hills" or "little shrubbery" from muine, a shrubbery, with the diminutive affix cán.
- Dominic Monaghan- Actor
- Michelle Monaghan- Actress
- Cameron Monaghan- Actor
- Patrick Monahan- Singer
- William Monahan- Screenwriter and Novelist
A census conducted in 1890 of Ireland states that an estimated 4,300 Irish citizens bear the name Monaghan.