The surnames Gleeson and Gleason developed from the Irish name O Glasain, which originated in East County Cork. The Gaelic prefix “O” means male descendant of, and Glasain derives from “glas,” literally meaning “green” in the sense of inexperience as opposed to the color. There are many variations of the name, including Gleason, Glisane, Glison, Glyssane, O’Gleasane and O’Glassane.
The Gleesons belonged to the ancient territory of Mac Ui Bhriain Aradh’s country, the area between Nenagh and Lough Derg in North County Tipperary. The name is still prominent in the area, but it has been carried all over the world.