First found in county Limerick, where they were seated from very ancient times at Bruree. Their hereditary territory were the lands along the banks of the river Maigues in that county. They were descended from Crom, the Chief of the Donovans, who built Crom Castle, and he in turn was descended anciently from Eoghan Mor (Eugene the Great), King of Munster. Amhailgadh II's son, Crom's great great grandfather, was a commander with King Brian Boru in the Battle of Clontarf against the Danes, and it was at this time through marriage that they lost the throne of Munster.

Suffering from poverty and racial discrimination, thousands of Irish Families left the island in the 19th century for North America aboard cramped passenger ships. The early migrants became settlers of small tracts of land, and those that came later were often employed in the new cities or transitional work camps. The largest influx of Irish settlers occurred with Great Potato Famine during the late 1840s. Although the immigrants from this period were often maligned when they arrived in the United States, they provided the cheap labor that was necessary for the development of that country as an industrial power. Early immigration and passenger lists have revealed many immigrants bearing the name O'Donovan: Daniell Donavan who settled in Barbados in 1680; Ann, Bat, Bridget, and Catharine Donavan all settled in Boston Massachusetts between 1847 and 1850; they also settled in Philadelphia, Pennsylvania Maryland, and New York.

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