An Irish surname, Reilly comes from the Gaelic terms ‘roghallach’ and ’raghailligh’ which refers to very outgoing and friendly people. The spelling variations for Reilly include Reilley, O’Reilly, Riley, Reilly and O’Riley. In Ireland the Reilly family name is very popular, ranking the 12th highest in the population. It originated in Counties Westmeath and Cavan. In England the Reilly surname covers most of the country and some of Wales. The few areas with higher Reilly populations include the city of London and Lancashire county. In Scotland just about all of the country has higher populations of the Reilly family name. Those with the highest percent are in Lanarkshire, Midlothian and Angus counties. Within the United States Reilly families began settling in Pennsylvania, New Jersey, Maryland, New York and Virginia. Famous: Maggie Reilly (singer from Scotland), Rick Reilly (sports broadcaster), James F. Reilly (astronaut), John C. Reilly (actor), Mike “Ike” Reilly (musician), Charles Nelson Reilly (comic actor and director), John “Long John” Reilly (early professional baseball player), Kelly Reilly (actress from England), David Reilly (singer), Paul C. Reilly (architect of NYC theaters), Donald Reilly (cartoonist) and Matthew John Reilly (author of action thrillers from Australia).