Trélex is a municipality in the district of Nyon in the canton of Vaud in Switzerland.
Trélex is first mentioned in 1145 as Trailai.
Trélex has an area, as of 2009, of 5.8 square kilometers (2.2 sq mi). Of this area, 3 km2 (1.2 sq mi) or 51.9% is used for agricultural purposes, while 1.98 km2 (0.76 sq mi) or 34.3% is forested. Of the rest of the land, 0.86 km2 (0.33 sq mi) or 14.9% is settled (buildings or roads), 0.01 km2 (2.5 acres) or 0.2% is either rivers or lakes.
Of the built up area, housing and buildings made up 8.3% and transportation infrastructure made up 4.3%. Power and water infrastructure as well as other special developed areas made up 2.1% of the area Out of the forested land, 33.0% of the total land area is heavily forested and 1.2% is covered with orchards or small clusters of trees. Of the agricultural land, 46.0% is used for growing crops and 4.3% is pastures, while 1.6% is used for orchards or vine crops. All the water in the municipality is in lakes.