This is an Anglicized form of the Old Gaelic "O Siodhachain". The Gaelic prefix "O" indicates "male descendant of", plus the personal byname "Siodhachain", a diminutive of "Siodhach", peaceful or "Siodach", gentle and courteous. Originally belonging to County Clare, this clan moved southwards to occupy Counties Cork, Kerry and Limerick, and it is in these counties that the name is most numerous today. It occupies seventy-fifth place in the list of Ireland's most widespread surname, together with the variant form Sheahan. It is interesting to note that a separate clan called O' Sheehan occupied territory in Ui Maine (mid Galway and South Rosscommon) in medieval times, but the name is rarely found in Connacht today. An interesting namebearer was Michael Sheehan (1870 - 1945), Archbishop of Sydney, who was associated with Kings College and the revival of the Irish language. A Coat of Arms granted to the Sheehan family is a blue shield, on a green base a silver dove holding in the beak an olive branch proper, the Crest being a silver dove holding in the beak an olive branch proper. The first recorded spelling of the family name is shown to be that of John Sheehan, of County Cork, which was dated 1659, in Petty's "Census' of Ireland", during the reign of Richard Cromwell, known as "The Lord Protector", 1658 - 1660. Surnames became necessary when governments introduced personal taxation. In England this was known as Poll Tax. Throughout the centuries, surnames in every country have continued to "develop" often leading to astonishing variants of the original spelling.