The name is found primarily in County Galway and County Limerick. The town of Gort, Ireland, was the decapitant of the family since at least the time of their ancestor, King Guaire Aidhne of the Ui Fiachrach Aidhne dynasty. Up until the late 1600s the O'Shaughnessys held the sub district of Uí Fiachrach Aidhne known as Cinéal nAedha na hEchtghe, which was also their clan name. Cinéal nAedha na hEchtghe / Kinelea consisted roughly of the civil parishes of Beagh, Kilmacduagh and Kiltartan and also parts of the civil parishes of Kibeacanty and Kilthomas. Their closest related kinsmen were the Ó Cathail / O Cahill clan, originally chiefs of eastern Kinelea, and the other clans of Uí Fhiachrach Aidhne the most prominent of which were the Ó hEidhin / O Hynes, Ó Cléirigh / O Cleary and Mac Giolla Cheallaigh / Kilkelly septs. Up until the mid 1600s the O'Hynes clan were still styled lords of Uí Fhiachrach Aidhne even though the O'Shaughnessys had become more powerfull than their kinsmen during this century. In the 1690s the O'Shaughnessys had their lands confiscated for supporting the Jacobite cause against William of Orange. A legal battle raged on into the first half of the 1700s between the O'Shaughnessys and the Prendergasts, the family who were granted the O'Shaughnessy lands, with the O'Shaughnessys eventually losing the case. The senior line of the O'Shaghnessys may have died out in the 1780s.
The last "de facto" O'Shaughnessy Lord of Kinelea died at Gort after returning home from the Battle of Aughrim in July 1691. Thousands of bearers of the name still survive both in their homeland and further abroad. Notable people with this surname include:
Edward Phillip Shaughnessy-United States lawyer and husband of Ellen Shaughnessy