The town of Gasny is located 6 km from Giverny, 10 km from Vernon, 18 km from Magny-en-Vexin, 23 km from Mantes-la-Jolie and 25 km from Les Andelys.
Le Mesnil Milon is the main hamlet of Gasny.
The nearest stations are Bonnières (9 km) and Vernon - Giverny located 10 km away.
The commune of Gasny, with its 2,941 inhabitants (1999 census), is the only commune with more than 1,000 inhabitants in the former canton of Écos, which has 13,178 inhabitants distributed in 23 communes.