The surname presents multiple independent clusters of origin (ceppi), arisen in different regions without direct relation between them.

It is considered that the surname could derive from the Latin baptismal name Bonifatius, that is, the one who has a good destiny (from the Latin fatum). Fatius is the abbreviated form that already appears in lists of Milanese citizens who in 1266 swore obedience to the Holy See. The diminutive Faciolus figures in Bergamo in 1156, in the list known as that of the Thousand Men of Bergamo. In 1237, in the codex of the capitular library of the Duomo of Monza, the form Faxolus appears already as a surname, corresponding to a peasant of Agrate.

E. Rossoni proposes an alternative etymology: the surname could derive from a nickname linked to the old dialectal term fasolo, which designates the bean, in turn from the Latin faseolus. The origin of the nickname could have been due to the memory of some particular episode or to the founder of the lineage having been a cultivator of that pulse.

As for its distribution, Rossoni notes that Fasoli presents three specific zones of presence in Italy: one in the provinces of Como, Milan, Lodi and Cremona; another in the Verona area; and a third in the Chieti area. The variant Fasolo, on the other hand, is clearly peculiar to the Veneto, with a main nucleus in Padua and its surroundings.