First found in Galway, and county Clare where they held a family seat from ancient times. They were descended from Olioll Olum, King of Munster who reigned about 130 A.D. and descended through a line of Chiefs and Kings to John O'Grady, alias O'Brady, who died in 1332 in the Clann territories of Fassaghmore in the county of Clare. His son, Sir Denis O'Grady alias O'Brady of Fassaghmore was knighted by King Henry VI of England. This great confusion of names continued into the 14th and 15th century and to make matters even more confusing the line frequently reverted from one spelling to the other. The Clann seat became established at Kilballyowen in county Limerick, and the present Chief of the Gradys (or Bradys) is one of the few Chiefs recognized in Ireland. He is Lieutenant Colonel Gerald Vogors de Courcy O'Grady. They were settled in Glenstal Abbey. Many of the name were also found in Cavan.

Irish immigrants began to leave the English-controlled Ireland in sizable numbers during the late 18th century. Many of these Irish immigrated to British North America or the United States in the hopes of gaining their own tract of farmland. This pattern of migration grew steadily until the 1840s when the Great Potato Famine caused a great exodus of immigrants to North America. These immigrants differed from their predecessors in that they were desperately fleeing the disease and starvation that plagued their homeland, and many were entirely destitute when they arrived in North America. Although these penniless immigrants were not warmly welcomed when they arrived, they were critical to the rapid development of the United States and what would become known as Canada. Many went to populate the western frontiers and others provided the cheap labor the new manufacturing sector and the building of bridges, roads, railways, and canals required. A thorough examination of immigration and passenger lists has revealed some of the earliest people to arrive in North America with name Brady or one of its variants: Andrew Brady, who arrived in Virginia in 1674; Daniel Brady, who was sent to America in 1741; Dennis Brady, who came to Philadelphia in 1746; Eleanor Brady, who came to Virginia in 1714.

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