The authors agree that this surname has a well-defined Friulian origin, with a historical presence in the Udine area, particularly in Moggio Udinese and Tolmezzo.

E. De Stefani places the original stem in Moggio Udinese, from where different branches spread towards the Carnia —the mountainous region of northern Friuli, in the province of Udine—, with a documented presence in Amaro, Tolmezzo, Plan di Coces (a frazione of Arta Terme), Caneva (a frazione of Tolmezzo) and Collina (a frazione of Forni Avoltri, from the late 18th century). The documentary attestation goes back at least to the early 18th century. As for the origin of the name, De Stefani proposes that it is an aphaeretic hypocoristic continuation of Bartolomeo (Latin Bartholomaeus), with the evolution Bortolatius > Tolatius > Tolazzi, through the fall of the initial syllable and the addition of the suffix -azzi. As an alternative reading, he notes that the related Venetan surname Tòlo could derive from aphaeretic forms such as (Alber)tòlo or (Rober)tòlo.

E. Rossoni agrees on the essentials, but specifies that the immediate base would be Tolač, a Slovenian aphaeretic form of a hypocoristic of Bartolazzo or Bertolazzo, in turn alterations of Bartolomeo. Rossoni also records the variant Tolazzo, of almost unique appearance, likewise located in the Udine area.