Val-d'Illiez is a municipality in the district of Monthey in the canton of Valais in Switzerland .

Val-d'Illiez has an area, as of 2009, of 39.3 square kilometers (15.2 sq mi). Of this area, 15.04 km2 (5.81 sq mi) or 38.3% is used for agricultural purposes, while 14.42 km2 (5.57 sq mi) or 36.7% is forested. Of the rest of the land, 1.62 km2 (0.63 sq mi) or 4.1% is settled (buildings or roads), 0.21 km2 (0.081 sq mi) or 0.5% is either rivers or lakes and 7.96 km2 (3.07 sq mi) or 20.3% is unproductive land.

Of the built up area, housing and buildings made up 1.8% and transportation infrastructure made up 1.8%. Out of the forested land, 29.0% of the total land area is heavily forested and 2.0% is covered with orchards or small clusters of trees.