First found in county Cavan, where they held a family seat from very ancient times.

Irish Families left their homeland in astonishing numbers during the 19th century in search of a better life. Although individual reasons vary, most of these Irish families suffered from extreme poverty, lack of work opportunities, and exorbitant rents in their homeland. Many decided to travel to Australia or North America in the hopes of finding greater opportunities and land. The Irish immigrants that came to North America initially settled on the East Coast, often in major centers such as Boston or New York. But like the many other cultures to settle in North America, the Irish traveled to almost any region they felt held greater promise; as a result, many Irish with gold fever moved all the way out to the Pacific coast. Others before that time left for land along the St. Lawrence River and the Niagara Peninsula, or the Maritimes as United Empire Loyalists, for many Irish did choose to side with the English during the American War of Independence. The earliest wave of Irish migration, however, occurred during the Great Potato Famine of the 1840s. An examination of early immigration and passenger lists has revealed many people bearing the O'Riley name: the families who settled in Newfoundland - in St. John's, Tilton Harbour, Placientia, Tickle Bay, Tilt Cove, and many more, between 1805 and 1871; James O'Reiley settled in New York in 1823.

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