The surname Dunn comes from the Gaelic word donn, which means "brown" The Gaelic form O'Duinn (the descendant of donn) is most commonly anglicized as Dunn, but is also written as Dunne. The Dunn family is of the same Celtic stock as the O'Connors and O'Dempseys-clans who trace their descendants from Rossa Failgeach, eldest son of Cathaoir Mor, king of Ireland in the second century. The Dunn sept stems from Riagan, tenth in lineal descent from Failgeach, the district ruled over by Riagan, located in County Leix, which became the ancestral home of the Dunns. In later times, their chieftains were known as Lords of Iregan. Irish bards praise the martial prowess and commanding stature of the Dunn warriors. They were undoubtedly conspicuous in history for their doughty resistance to the encroachment of Anglo-Norman invaders who held lands in the pale boarding their territory. The Dunns were in the forefront of every battle for Irish nationalism. They suffered heavily in the bitter and prolonged struggle against Cromwell. In the next generation, they espoused the Stuart cause, and the head of the family was killed in the Battle of Aughrim. With the fall of the Stuarts, the lands of the Dunns were confiscated, and their fighting men who survived followed Sarsfield and the "wild geese" to fight in the ranks of the Irish Brigade in France. Many of them served with distinction in the regiments of O'Donnell, Lord Clare, and Walsh up to the days of the French Revolution. The name Dunn is twenty-seventh in the list of commonest surnames in Ireland. It is widespread in the United States also. Representatives of the family have achieved prominence in the literary, political, and religious life of our country.