The authors agree that the surname is of Germanic origin. E. Rossoni notes that it could derive from the Gothic name Goar or Goiaricus, although he also considers possible a derivation from the propitiatory name Guarisco or from the aphaeresis of DioGuarisci. He records early documentation in Bianzone, in the Sondrio area, in a deed of 1436, and in Bergamo in a deed of 1506. As an example of its fixing as a surname, he mentions a Francesco Guarisco among the Patricians of Ferrara in the second half of the 16th century.

V. Blunda specifies that the surname derives from the Germanic personal name Warisk, an adjectival form built on the root wara ("watchfulness, care") with the Germanic suffix -isk, the same one that gave modern German -isch and Italian -esco, with an adjective-forming function.

As for geographical distribution, Rossoni indicates that Guareschi appears to be specific to the Parma area; Guarischi, very rare, is typical of the area south of Milan and of the Pavia and Lodi areas; and Guarisco would show three cores: in the Milan and Como areas, in that of Brescia, and in Sicily, in the province of Agrigento.

Blunda stresses that the writer and journalist Giovannino Guareschi (1908–1968), a native of Emilia-Romagna, created the celebrated Don Camillo and Peppone saga, set in the Po valley of post-war Italy.