William Cassidy may refer to: Bill Cassidy (born 1957), American politician William A. Cassidy, American geologist Bill Cassidy (footballer, born 1917) (1917–1962), English footballer with Gateshead Bill Cassidy (footballer, born 1940) (1940–1995), Scottish footballer with Rotherham United, Brighton & Hove Albion, Detroit Cougars and others William F. Cassidy (1908–2002), American military commander