I have begun this Forum to take account of one of the spellings of the name. The variations of SHEERAN/SHEERIN/SHERAN, as far as a article once published in 'Ireland's Own' (published in Wexford) is concerned, 'take their present name from the original Irish form O SIRIN. There was a family of this name in Co. Cork who now seem to be extinct, and the majority of the people with this surname come from a Co. Donegal family who later spread down as far south as Laois. MacLysaght thinks that the SYRON family in Co. Mayo may be of the same stock.'
The Mac Lysaght mentioned above, in a further article (origin of which I have mislaid!) also says 'There are five modern variants of this name, SHEERAN and SHEERIN being the most numerous ... Eighteen century wills indicate that the name was [numerous in many counties] but none are from the Co. Cork diocese ... as many as 56 families in Queen's Co. (Leix)'.
My own forebear - Michael SHEARAN - arrived in England some time before 1872: the date of his son Thomas' marriage in Leeds, Yorkshire. Thomas was shown on the 1881 census as having been born in Co. Kildare; his age was then 32, so his birth may well have been in 1848/49. The same census index shows him to be the only SHEARAN in the whole county of Yorkshire. Some other research points up the fact that some SHEARANs arrived in both North and South Wales.