First found in County Cork where they were anciently seated at Muskerry, later moving to Limerick, Kildare and Dublin.

Many destitute Irish families in the 18th and 19th centuries decided to leave their homeland, which had in many ways been scarred by English colonial rule. One of the most frequent destinations for these families was North America where it was possible for an Irish family to own their own parcel of land. Many of the early settlers did find land awaiting them in British North America, or even later in America, but for the majority of immigrants that arrived as a result of the Great Potato Famine of the late 1840s the ownership of land was often a long way off. These Irish people were initially put to work on such industrial projects as the building of bridges, canals, and railroads, or they worked at manufacturing positions within factories. Whenever they arrived, the Irish made enormous contributions to the infant nations of Canada and the United States. Some of the earliest immigrants to bearer the name of Donegan were found through extensive research of immigration and passenger lists: Thomas Donegan, the Earl of Limerick, who became Governor of New York from 1683 to 1691. Patrick Donegan settled in Maryland in 1742; Andrew, Charles, Christopher, John, Mathew, Patrick, Phillip, Thomas Donegan, all arrived in Pennsylvania between 1839 and 1878.

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