The Irish surname Reily is an anglicized form of Gaelic Ó Raghailligh meaning “descendant of Raghailleach,” The Old Irish  Roghallach, is a personal name of unexplained etymology. This is the name of a chieftain family in County Cavan, related to the O’Rourkes. The celebrated Count Alexander O'Reilly from Meath distinguished himself first in the Austrian service and then in the Spanish army. He put down a rebellion in Louisiana where he became governor. The O'Reillys have a reputation as astute financiers. In the 15th Century they devised their own coinage. A "Reilly" has come to signify a coin of useful value.