This interesting surname is of Anglo-Saxon and Irish origin, and has two possible sources, the first being locational from any of the various place so called in England, derived from the Olde English pre 7th Century "crawe", crow, and "leah", wood, clearing. The second source is an Anglicization of the Gaelic "O'Cruadhlaoich", descendant of "Cruadhlaoch", a personal name composed of the elements "cruadh", hardy, and "laoch", hero. The O'Crowley sept began as an off-shoot of the MacDermots of Mylurg (Co. Roscommon), their eponymous ancestor was Cruadhlaoch, who emigrated to a territory near Dunmanway, Co. Cork; in due course they became a distinct sept with a recognised chief residing at Kilshallow. Many of the sept were employed as professional soldiers, and usually fought for the MacCarthys. Today the surname is very rare in Co. Roscommon, and is mainly found in West Cork. The modern surname can be found as (O)Crowley, Crawley, Croley, Crolly and Crolla. Among the recordings in Ireland the marriage of Cornelius Crowley and Joanna McDonald on March 11th 1766, at St. Munchin, Co. Limerick. The first recorded spelling of the family name is shown to be that of Pagan de Craweleia, which was dated 1130, in the "Pipe Rolls of Berkshire", during the reign of King Henry 1, known as "The Lion of Justice", 1100 - 1135. 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.