Troistorrents (French pronunciation: [tʁwatɔʁɑ̃]; Arpitan: Trètorrent) is a municipality in the district of Monthey in the canton of Valais in Switzerland .

Troistorrents has an area, as of 2009, of 37 square kilometers (14 sq mi). Of this area, 13.54 km2 (5.23 sq mi) or 36.6% is used for agricultural purposes, while 19.14 km2 (7.39 sq mi) or 51.8% is forested. Of the rest of the land, 2.72 km2 (1.05 sq mi) or 7.4% is settled (buildings or roads), 0.21 km2 (0.081 sq mi) or 0.6% is either rivers or lakes and 1.34 km2 (0.52 sq mi) or 3.6% is unproductive land.

Of the built up area, housing and buildings made up 4.6% and transportation infrastructure made up 2.3%. Out of the forested land, 47.5% of the total land area is heavily forested and 2.9% is covered with orchards or small clusters of trees.