Isorno is a former municipality in the district of Locarno in the canton of Ticino in Switzerland . On 10 April 2016 the former municipalities of Vergeletto , Gresso , Mosogno and Isorno merged into the municipality of Onsernone .

The former municipality was created in 2001 by a merger of Auressio , Berzona and Loco.

Auressio is first mentioned in 1233 as Oraxio. Berzona is first mentioned in 1265 as Berzona. Loco is first mentioned in 1224 as Loco and was also known as Luogo.