IrishCentral has put together a list of the top 100 common Irish surnames.
(O) Whelan Ó Faoláin (faol, wolf). A variant form of Phelan numerous in the country between Co. Tipperary and Co. Wexford. Whelan is also sometimes an abbreviation of Whelehan and occasionally a synonym of Hyland. Whelan is rare in Ulster.