The authors agree that the surname derives from the term guercio, meaning "one-eyed" or "poor-sighted", originally used as a nickname. E. De Felice notes that the nickname has regional variants: the northern forms guerzo and sguerzo, the Emilian guerz, the Ligurian guerzu, and the forms gusrso and guersu.

E. Rossoni proposes that the surname could also derive from the medieval names Guercius and Guercinus, documented as early as the 13th century in the Annales Ianuenses (1280–1294). According to Rossoni, the form Guerci appears to originate in the strip linking Milan with Genoa, passing through the Pavia and Alessandria areas.

De Felice indicates that the surname has a sporadic distribution in Italy, with the form Guercio predominant in the south, Del Guercio concentrated in Tuscany, and the variants Guerzi, Sguerzi and Ghersi proper to the north. Rossoni, for his part, places the form Guercio in areas of Ancona, Rome, Salerno, Potenza and Cosenza, with a notable presence in Sicily, especially in Palermo, Lentini and Carlentini, in the Syracuse area.