Gemonio is a comune (municipality) in the Province of Varese in the Lombardy region of Italy, located about 60 kilometres (37 mi) northwest of Milan and about 14 kilometres (9 mi) northwest of Varese. As of 31 December 2022, it had a population of 2,851 and an area of 3.7 square kilometres (1.4 sq mi).

Gemonio borders the following municipalities: Azzio, Besozzo, Brenta, Caravate, Cittiglio, Cocquio-Trevisago.

In Gemonio lives Umberto Bossi, an Italian politician.