The authors agree that this is a typically Sicilian surname, with a presence concentrated mainly in the Catania area. E. Rossoni documents its antiquity with a deed of 1631 in Palermo, in which the Senate commissioned certain works from the master silversmith Matteo Lo Castro.

F. Miranda proposes that the surname probably derives from place names containing the root castr-, such as Castrovillari, Castrocaro, Castrogiovanni or Castro Marina. The term castro, in turn, comes from the Latin castrum, meaning "fortified place". Miranda adds that in Sardinia the term castro designated both ancient fortresses and the nuraghi, structures regarded as the oldest of Sardinian civilization.

According to Miranda, the surname shows multiple independent clusters of origin (ceppi), arisen in different regions without direct relation between them. The main core is located in Sicily, especially in the Catania, Messina, Trapani, Palermo and Caltanissetta areas. Lesser cores appear in northern Italy, in regions such as Lombardy, Piedmont, Emilia-Romagna and Liguria, as well as in Lazio, Tuscany and Campania.