The authors agree that the surname derives from the name of Germanic origin Magnulfus (also documented as Manulfus or Maginulfus), of Lombard tradition, formed from the elements magin- ("strength, power") and wulf- ("wolf"), with the approximate sense of "strong and powerful wolf".

E. De Felice notes that the name is documented from early times: it appears as early as 715 in Pisa and in 744 in Farfa, in the Sabina. He considers the surname rare and sporadic in Italy generally, although frequent in Tuscany.

E. Rossoni specifies that Magnolfi is typical of the areas of Prato, Florence, Calenzano and Sesto Fiorentino. He further records the variants Mainolfi, present in Rome, Mentana and in the Avellino area (Rotondi and Cervinara), with a scattered presence in Campania; and he notes that the Campanian core could also derive from the place name Mainolfo, in the province of Salerno. The forms Mainolfo and Mangiolfi, of almost isolated occurrence, are probably attributable to transcription errors for Magnolfi.