The scholars consulted agree that this surname derives from the given name Lattanzio, itself linked to the Latin cognomen Lactantius. E. De Felice notes that the precise origin of that cognomen is uncertain, and points as a possible etymon to Lactans, a Roman deity associated with vegetation. De Felice further specifies that the name was revived during the humanist period.

Both De Felice and E. Rossoni recall the Latin writer known as Lattanzio — a significant figure among the great apologists and Fathers of the Church — though they identify him slightly differently: De Felice refers to him as Firmiano Lattanzio, active around the year 300, while Rossoni gives his full name as Lucius Caelius Firmianus Lactantius (240–320).

Rossoni distinguishes two forms of the surname according to their geographical distribution. The variant Lattanzi is characteristic of a central strip of Italy comprising the Marche, Umbria, Abruzzo, and especially Lazio, with a presence also in the area of Bari. The variant Lattanzio, considerably less widespread, is concentrated in Abruzzo, Molise, and the areas of Foggia and Bari. De Felice, for his part, places the surname more broadly in central and peninsular southern Italy.