Gresso is a former municipality in the district of Locarno in the canton of Ticino in Switzerland. The municipality was formed in 1882 by splitting from Vergeletto. On 10 April 2016 the former municipalities of Vergeletto, Gresso, Mosogno and Isorno merged into the municipality of Onsernone.

Vergeletto 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.