O'Shannassy could refer to:
O'Shannassy River, a river in Victoria, Australia O'Shannassy Reservoir, a reservoir in Victoria, Australia, created by damming the O'Shannassy River Bob O'Shannassy (born 1949), Australian cricketer and rules footballer Teigan O'Shannassy (born 1999), Australian netball player
See also O'Shaughnessy, Irish surname