Scholars agree that this surname originates in the Italianization of the Spanish surname García, the most widespread surname on the Iberian Peninsula, and constitutes a prosthetic form of Garsìa and Grassìa. The addition of the prefix In- at the beginning is a very frequent phenomenon in the surnames of southern Italy, as seen in parallel pairs such as Calcaterra/Incalcaterra, Cardona/Incardona, Serra/Inserra, and Zerillo/Inzerillo.

E. Rossoni notes that the surname could also have a Judeo-Sephardic origin. The variant Ingarsia is very rare and is found specifically on the island of Favignana, in the area of Trapani, while Ingrassia is very widespread throughout Sicily, especially in the areas of Trapani, Palermo, and Catania.

F. Miranda goes deeper into the etymology of García and proposes two hypotheses: that it derives from a place name — specifically from the municipality of García, in the province of Tarragona, Catalonia, of probable pre-Roman origin — or that it comes from the Basque term (h)artz, meaning "bear" (or "fox"). Miranda further explains that Grassìa is a metathesis in which the syllable gar becomes gra, with the s serving as a phonetic adaptation of the Spanish c.

G. P. Holmes limits the etymology of García to the meaning "male fox," without developing further hypotheses.