Diegan is a transposed spelling of the original Gaelic name O Duibhginn, "dubh" meaning black and "cinn" (head). The name may therefore be translated as "a descendant of the black or dark haired people". "O" or "ui" is the Gaelic word for grandson or male descendant. In its anglicized forms the name appears as Diegan, Duigan and Deighan. The most usual form however, is Deegan. The name is most numerous to-day in the province of Leinster in the counties of Laois and Offaly. Petty's census recorded it as Duigen in 1659. An interesting name bearer was James Robertson Duigan (1882 - 1951) who is commemorated by a monument at Lancefield, Victoria, for a pioneering Australian flight in a plane built by himself. The first recorded spelling of the family name is shown to be that of O'Doygan. which was dated 1559, Recorded by the "Fiants census". during the reign of Queen Elizabeth 1, known as "Good Queen Bess" 1558 - 1603. 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.