Saint-Prex (French pronunciation: [sɛ̃.pʁɛks]) is a municipality in the Swiss canton of Vaud, located in the district of Morges.

In 1973, St-Prex was awarded the Wakker Prize for the development and preservation of its architectural heritage.

Saint-Prex is first mentioned in 885 as Sanctus Prothasius.

The town was founded with the construction of the chateau in 1234AD. The bourg (old town) forms a peninsula extending from the north shore of Lake Geneva. In recent years the commerce of the town has mostly moved to outer areas. St-Prex is a port for the CGN lake steamers in summer.

Saint-Prex has an area, as of 2009, of 5.5 square kilometers (2.1 sq mi). Of this area, 2.9 km (1.1 sq mi) or 52.5% is used for agricultural purposes, while 0.46 km (0.18 sq mi) or 8.3% is forested. Of the rest of the land, 2.12 km (0.82 sq mi) or 38.4% is settled (buildings or roads), 0.02 km (4.9 acres) or 0.4% is either rivers or lakes.

Of the built up area, industrial buildings made up 2.9% of the total area while housing and buildings made up 20.8% and transportation infrastructure made up 9.2%. Power and water infrastructure as well as other special developed areas made up 2.5% of the area while parks, green belts and sports fields made up 2.9%. Out of the forested land, all of the forested land area is covered with heavy forests. Of the agricultural land, 36.2% is used for growing crops and 2.5% is pastures, while 13.8% is used for orchards or vine crops. All the water in the municipality is in lakes.

The municipality was part of the Morges District until it was dissolved on 31 August 2006, and Saint-Prex became part of the new district of Morges.

The municipality is located along Lake Geneva. It consists of the village of Saint-Prex and the hamlets of Les Iles, Beaufort, Senaugin and Fraidaigue. The currently abandoned villages of Dracy and Marcy are also in the municipal area.

The blazon of the municipal coat of arms is Gules, a Fleur-de-lys Argent.

Saint-Prex has a population (as of December 2020) of 5,855. As of 2008, 32.8% of the population are resident foreign nationals. Over the last 10 years (1999–2009 ) the population has changed at a rate of 25%. It has changed at a rate of 16.3% due to migration and at a rate of 9.1% due to births and deaths.

Most of the population (as of 2000) speaks French (3,472 or 82.5%), with German being second most common (212 or 5.0%) and Italian being third (137 or 3.3%).

Of the population in the municipality 848 or about 20.1% were born in Saint-Prex and lived there in 2000. There were 1,266 or 30.1% who were born in the same canton, while 773 or 18.4% were born somewhere else in Switzerland, and 1,213 or 28.8% were born outside of Switzerland.

In 2008 there were 43 live births to Swiss citizens and 21 births to non-Swiss citizens, and in same time span there were 22 deaths of Swiss citizens and 3 non-Swiss citizen deaths. Ignoring immigration and emigration, the population of Swiss citizens increased by 21 while the foreign population increased by 18. There were 2 Swiss men and 1 Swiss woman who immigrated back to Switzerland. At the same time, there were 59 non-Swiss men and 66 non-Swiss women who immigrated from another country to Switzerland. The total Swiss population change in 2008 (from all sources, including moves across municipal borders) was an increase of 45 and the non-Swiss population increased by 106 people. This represents a population growth rate of 3.1%.

The age distribution, as of 2009, in Saint-Prex is; 629 children or 12.5% of the population are between 0 and 9 years old and 562 teenagers or 11.2% are between 10 and 19. Of the adult population, 578 people or 11.5% of the population are between 20 and 29 years old. 842 people or 16.7% are between 30 and 39, 864 people or 17.1% are between 40 and 49, and 652 people or 12.9% are between 50 and 59. The senior population distribution is 510 people or 10.1% of the population are between 60 and 69 years old, 247 people or 4.9% are between 70 and 79, there are 129 people or 2.6% who are between 80 and 89, and there are 27 people or 0.5% who are 90 and older.

As of 2000, there were 1,750 people who were single and never married in the municipality. There were 2,008 married individuals, 175 widows or widowers and 277 individuals who are divorced.

As of 2000, there were 1,799 private households in the municipality, and an average of 2.2 persons per household. There were 613 households that consist of only one person and 84 households with five or more people. Out of a total of 1,835 households that answered this question, 33.4% were households made up of just one person and there were 7 adults who lived with their parents. Of the rest of the households, there are 529 married couples without children, 527 married couples with children There were 94 single parents with a child or children. There were 29 households that were made up of unrelated people and 36 households that were made up of some sort of institution or another collective housing.

In 2000 there were 373 single family homes (or 52.5% of the total) out of a total of 710 inhabited buildings. There were 216 multi-family buildings (30.4%), along with 72 multi-purpose buildings that were mostly used for housing (10.1%) and 49 other use buildings (commercial or industrial) that also had some housing (6.9%). Of the single family homes 66 were built before 1919, while 46 were built between 1990 and 2000. The most multi-family homes (63) were built before 1919 and the next most (28) were built between 1961 and 1970. There were 12 multi-family houses built between 1996 and 2000.

In 2000 there were 1,983 apartments in the municipality. The most common apartment size was 3 rooms of which there were 604. There were 129 single room apartments and 411 apartments with five or more rooms. Of these apartments, a total of 1,753 apartments (88.4% of the total) were permanently occupied, while 190 apartments (9.6%) were seasonally occupied and 40 apartments (2.0%) were empty. As of 2009, the construction rate of new housing units was 1.8 new units per 1000 residents. The vacancy rate for the municipality, in 2010, was 0.34%.

The historical population is given in the following chart:

The Swiss Reformed Church of Notre-Dame is listed as a Swiss heritage site of national significance. The entire old city of Saint-Prex is part of the Inventory of Swiss Heritage Sites.

In the 2007 federal election the most popular party was the SVP which received 26.04% of the vote. The next three most popular parties were the SP (19.35%), the Green Party (14.13%) and the FDP (14.06%). In the federal election, a total of 1,188 votes were cast, and the voter turnout was 46.5%.

As of  2010, Saint-Prex had an unemployment rate of 4.5%. As of 2008, there were 51 people employed in the primary economic sector and about 15 businesses involved in this sector. 740 people were employed in the secondary sector and there were 31 businesses in this sector. 966 people were employed in the tertiary sector, with 126 businesses in this sector. There were 2,321 residents of the municipality who were employed in some capacity, of which females made up 44.6% of the workforce.

In 2008 the total number of full-time equivalent jobs was 1,481. The number of jobs in the primary sector was 36, of which 35 were in agriculture and 1 was in fishing or fisheries. The number of jobs in the secondary sector was 718 of which 669 or (93.2%) were in manufacturing and 48 (6.7%) were in construction. The number of jobs in the tertiary sector was 727. In the tertiary sector; 167 or 23.0% were in wholesale or retail sales or the repair of motor vehicles, 24 or 3.3% were in the movement and storage of goods, 25 or 3.4% were in a hotel or restaurant, 15 or 2.1% were in the information industry, 9 or 1.2% were the insurance or financial industry, 21 or 2.9% were technical professionals or scientists, 137 or 18.8% were in education and 228 or 31.4% were in health care.

In 2000, there were 533 workers who commuted into the municipality and 1,697 workers who commuted away. The municipality is a net exporter of workers, with about 3.2 workers leaving the municipality for every one entering. About 2.3% of the workforce coming into Saint-Prex are coming from outside Switzerland, while 0.1% of the locals commute out of Switzerland for work. Of the working population, 13.9% used public transportation to get to work, and 66% used a private car.

Ferring Pharmaceuticals, a multinational pharmaceutal company, is headquartered in Saint-Prex.

Vale, a Brazilian mining company, has a regional office in Saint-Prex.

From the 2000 census, 1,638 or 38.9% were Roman Catholic, while 1,521 or 36.1% belonged to the Swiss Reformed Church. Of the rest of the population, there were 48 members of an Orthodox church (or about 1.14% of the population), there was 1 individual who belongs to the Christian Catholic Church, and there were 220 individuals (or about 5.23% of the population) who belonged to another Christian church. There were 9 individuals (or about 0.21% of the population) who were Jewish, and 124 (or about 2.95% of the population) who were Islamic. There were 8 individuals who were Buddhist and 12 individuals who belonged to another church. 538 (or about 12.78% of the population) belonged to no church, are agnostic or atheist, and 180 individuals (or about 4.28% of the population) did not answer the question.

In Saint-Prex about 1,436 or (34.1%) of the population have completed non-mandatory upper secondary education, and 775 or (18.4%) have completed additional higher education (either university or a Fachhochschule). Of the 775 who completed tertiary schooling, 50.8% were Swiss men, 22.8% were Swiss women, 13.5% were non-Swiss men and 12.8% were non-Swiss women.

In the 2009/2010 school year there were a total of 632 students in the Saint-Prex school district. In the Vaud cantonal school system, two years of non-obligatory pre-school are provided by the political districts. During the school year, the political district provided pre-school care for a total of 631 children of which 203 children (32.2%) received subsidized pre-school care. The canton's primary school program requires students to attend for four years. There were 336 students in the municipal primary school program. The obligatory lower secondary school program lasts for six years and there were 289 students in those schools. There were also 7 students who were home schooled or attended another non-traditional school.

As of 2000, there were 120 students in Saint-Prex who came from another municipality, while 227 residents attended schools outside the municipality.

The municipality has a railway station, St-Prex, on the Lausanne–Geneva line. It has regular service to Allaman, Lausanne, and Palézieux.

• Annie Leuch-Reineck (1880 - 1978 in Saint-Prex) a Swiss mathematician and women's rights activist
• André Bugnon (born 1947) politician, mayor of Saint-Prex 1990 to 2002, member of the Swiss National Council

• Official website
• CGN Compagnie Générale de Navigation sur le lac Léman