Gemonio is a comune (municipality) in the Province of Varese in the Lombardy region of Italy, located about northwest of Milan and about northwest of Varese. As of 31 December 2022, it had a population of 2,851 and an area of .
Gemonio borders the following municipalities: Azzio, Besozzo, Brenta, Caravate, Cittiglio, Cocquio-Trevisago.
In Gemonio lives Umberto Bossi, an Italian politician.