The authors agree that the surname derives, by aphaeresis, from the term allocco —a nocturnal bird of prey (the tawny owl)— whose fixed stare and unhurried bearing were popularly read as a sign of dullness. Applied as a nickname to people of slow understanding or bewildered reactions, it ended up becoming a surname.

E. Rossoni locates the surname in the Florence area, in that of Perugia —with a scattered presence in Città di Castello, Magione and Umbertide— and in Rome. He also notes the variant Locco, very rare, typical of the Cosenza area, especially of Bisignano. He further adds an alternative and less likely etymology: the archaic term locco, which designated a thick liquorice syrup prescribed for throat complaints, although he regards this derivation as secondary to that of the bird.

V. Blunda describes it as a surname of Sicilian dialect root and specifies that the source word is lòccu, with the meaning "silly, foolish, simple-minded". Although the semantic motivation coincides with the one noted by Rossoni, Blunda anchors the surname specifically in Sicily and stresses the dialect character of the base form.