This name, which is particularly prevalent in the Co Louth area of eastern Ireland, comes from the Irish word cearbhaill, which in its literal translation means 'slaughter' but in a more acceptable translation means 'warlike champion'. There were several different septs of the Carroll clan; the most important ones were those of Ely O'Carroll and Oriel, with minor septs in Co Leitrim and Co Kerry. A much older connection with the name can be seen in the village of Louth, eight miles south-west of Dundalk. Here can be seen the ruins of St Mary's Abbey, built long before Anglo-Norman times and refurbished in 1148 by Donough O'Carroll, the Prince of Oriel, who also endowed Mellifont Abbey, just west of Drogheda.

One of the main fortresses of the O'Carrolls is Leap Castle, near Coolderry in Co Offaly. The castle was burned during the troubles in 1922 but the ruins are extensive. It is said to be the most haunted house in Ireland.