Saint-Cergue is a municipality in the district of Nyon in the canton of Vaud in Switzerland.
Saint-Cergue is first mentioned in 1110 as ecclesiam Sancti Cyrici.
Saint-Cergue has an area, , of . Of this area, or 27.6% is used for agricultural purposes, while or 66.0% is forested. Of the rest of the land, or 5.8% is settled (buildings or roads) and or 0.5% is unproductive land.
Of the built up area, housing and buildings made up 3.3% and transportation infrastructure made up 2.2%. Out of the forested land, 62.6% of the total land area is heavily forested and 3.4% is covered with orchards or small clusters of trees. Of the agricultural land, 0.0% is used for growing crops and 2.1% is pastures and 25.5% is used for alpine pastures.
The municipality was part of the Nyon District until it was dissolved on 31 August 2006, and Saint-Cergue became part of the new district of Nyon.
The municipality is located in the Nyon district, on the road over the Col de la Givrine. The town consists of the village of Saint-Cergue and of the part of the hamlet of La Cure which since the treaty of Dappes of 1862 belongs to Switzerland and straddles the Swiss-French border.
The blazon of the municipal coat of arms is Per pale Or and Gules, dexter a tower Sable lined Argent crowned with a Mullet of Five Argent, sinister a Pine-tree vert, both on overall a Mount Vert.
Saint-Cergue has a population () of . , 27.6% of the population are resident foreign nationals. Over the last 10 years (1999–2009 ) the population has changed at a rate of 25.1%. It has changed at a rate of 21.3% due to migration and at a rate of 3.9% due to births and deaths.
Most of the population () speaks French (1,379 or 86.1%), with German being second most common (79 or 4.9%) and English being third (67 or 4.2%). There are 15 people who speak Italian and 2 people who speak Romansh.
The age distribution, , in Saint-Cergue is; 158 children or 8.1% of the population are between 0 and 9 years old and 259 teenagers or 13.3% are between 10 and 19. Of the adult population, 195 people or 10.