Anciently the O'Hanlons were cited as chiefs of Ui Meith Tiri, "now the barony of Orior" in Armagh, who held the office of hereditary standard bearers of Ulster. In today's words, this means that the O'Hanlons were chiefs of Orior in the baronies of Upper and Lower Orior in Armagh. They are also found in the O'Neilland barony.
In modern times the name has spread further. In the 1890 birth index, "O'Hanlon" had 22 recorded births in its homeland of Armagh and in County Dublin. Hanlon, without the "O", ha 95 births in Dublin, Kerry, Louth and Wexford.
In the 1659 census, both O'Hanlen and O'Hanlon were principal names of Armagh as might be predicted. Hanlon was as well a principal name of Kildare and found in Louth at the time, too.
Rev. John Cannon O'Hanlon (1821-1905), was the author of "Lives of the Irish Saints" among many other published works.