Cassidy (Irish: Ó Caiside / Ó Casaide) is a common Irish surname and is sometimes used as a given name. The surname translates to 'descendent of Caiside'. Variations include: Cassady, Cassiday, Cassedy and Cassedey. The family was a sept of County Fermanagh. The Caisides were originally a medical family, who were hereditary physicians to the Maguires.
Cassidy may refer to the following: