The authors agree that this surname is peculiar to Lombardy and is linked to place names of that region. E. De Felice notes that it was formed from the place names Casate, in the Milan area, and Casatenovo, in the Como area. E. Rossoni specifies that its area of greatest presence covers the Milan, Como, Lecco and Bergamo areas, with an additional presence in the Florence area, and proposes that it could derive from a nickname related to the place name Casatenovo, in the Lecco area.

The surname is considered to have very old roots and possibly linked to a Roman predial place name. Surnames in Italy documents that in 1102 the family already appears in Lombard registers, and that in 1337 it was included in the Milanese list. Its presence in Monza is also recorded from 1326, and a mention of Gerolamo da Casate in 1483 as aulicus noster —"our courtier"— on the part of Gian Galeazzo Maria Sforza.

Among the historical figures associated with the surname, Rossoni and Surnames in Italy agree in highlighting Count Gabrio Casati, who in 1848, during the Five Days of Milan, served as president of the Provisional Government of that city.