Last name Касий (Cassi 
, Kasy 
, Kasij 
) , around the world, is quite a rare family name. The surname Касий is habitual in Italy, where it is quite a rare surname, Argentina, where it is a rare surname, and Uruguay. In absolute terms, it is the most numerous in Italy, Argentina, and the United States. Likewise, Касий is the forename as well as the last name.