Origen: Irlandés. Esos escribientes en Irlanda durante a Edad media los nombres registrados como ellos sonaron simplemente porque sus portadores fueron analfabetos. Consecuentemente, en esta era muchas personas fueron registradas bajo deletreos diferentes cada vez que su nombre fue anotado. Encontrados primero en Ulster donde ellos tuvieron un asiento de la familia de tiempos muy antiguos. The clan from whom the McCool family descends began among the ancient Dalriadan tribe of the west coast of Scotland. Their name comes from the Gaelic Patronymic name Mac Cathmhaoil "son of Cathmhaol," a personal name composed of the elements "cath," meaning "battle," and "maol," meaning "chief." First found in Argyllshire (Gaelic erra Ghaidheal), the region of western Scotland corresponding roughly with the ancient Kingdom of Dál Riata, in the Strathclyde region of Scotland, now part of the Council Area of Argyll and Bute, where they were seated from early times and their first records appeared on the census rolls taken by the early Kings of Britain to determine the rate of taxation of their subjects.

Variantes: McCoole, Cooley, Cooling, Cowley, Cully, Colly, McCooley, Coaley, Coolyng, Couley, Colley, McCowley, Cooleng, McCoolay, Coolay, Collay, Cullay, Cowleigh, Culleigh y otros.