Recorded as O' Sheahan, O' Sheehan, Sheahan, Sheehan, and others, this is a famous Irish surname,. It deribves from the ancient Gaelic O' Siodhachain. The prefix O' indicates the "male descendant of", to which was added the personal byname Siodhachain, meaning the son or kinsman of the gentle one. Originally belonging to County Clare, the clan moved southwards in the 16th century to occupy part of Counties Cork, Kerry and Limerick, and it is in these counties that today the name is most numerous today. It occupies seventy-fifth place in the list of Ireland's most widespread surname. 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, although now seem to be extinct or nearly so. An interesting namebearer was Michael Sheehan (1870-1945), Archbishop of Sydney, Australia and who was associated with Ring College, and the attempted revival of the Irish language. In Canada the christening was recorded Patrick Henry the son of Patrick Sheehan, on April 11th 1838 at Peterborough, Ontario. The first recorded spelling of the family name is shown to be that of John Sheehan of County Cork, which was dated 1659, Petty's 'census' of Ireland. during the reign of Richard Cromwell, '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.