 Born in the village of Moynalty in County Meath of the United Kingdom of Great Britain and Ireland, Peter O'Reilly was ordained a priest on June 24, 1877.On July 3, 1900 Pope Pius X appointed him as the Titular Bishop of "Lebedus" and Auxiliary Bishop of Peoria.He was consecrated a bishop by Archbishop Sebastiano Martinelli, O.S.A., the Apostolic Delegate to the United States, on September 21, 1900.