Sheehan, Sheahan, ó Síodhacháin, ó Síocháin A Gaelic surname meaning descendant of Síodhachán, which personal name was a diminutive of Síodhách meaning ‘peaceful’. A sept of Dál gCais. A sept of Uí Mhaine, who were followers of ó Ceallaigh (O’Kelly). In 1890 Sheehan was the seventy-seventh most numerous surname and the estimated number of bearers was 9,600. In that year the surname was chiefly found in Cork, Kerry and Limerick. Half of the Munster entries were to be found in Cork (97 births). In the United States Sheehan is the 9,501st most numerous surname with an estimated 2,750 bearers. It is numerous in the states of Connecticut, and Massachusetts.
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