O'Reilly was born in New York City to Irish Catholic parents William and Angela O'Reilly, from Brooklyn, New York and Bergen County, New Jersey, respectively. His father was an accountant for the oil company Caltex. In 1951, his family moved to East Meadow on Long Island.[4] After graduating from Chaminade High School, a private Catholic boys high school in Mineola, New York in 1967, O'Reilly attended Marist College, a small, co-educational private (and at the time, Catholic) institution in Poughkeepsie, New York. While at Marist, O'Reilly played punter in the National Club Football Association,[5] and was also a columnist and feature writer for the school's newspaper, The Circle. As an honors student majoring in history, he spent his junior year of college abroad, attending Queen Mary College at the University of London.[6] O'Reilly received his B.A. in History in 1971. He played semi-professional baseball during this time as a pitcher for the Brooklyn Monarchs, and had an unsuccessful tryout with the American professional baseball team, the New York Mets.