Originally a North American name bestowed in honour of the American engine driver and folk hero ‘Casey’ Jones (1863–1900), who saved the lives of passengers on the ‘Cannonball Express’ at the expense of his own. He was baptized Johnathan Luther Jones in Cayce, Kentucky, and acquired his nickname from his birthplace. As a girl's name it is a variant of Cassie. In recent decades it has become equally popular in Britain, particularly as a name for girls. In part, this may reflect a transferred use of the Irish surname, a reduced Anglicized form of Ó Cahasaigh ‘descendant of Cathasach’.