Lonay is a municipality in the Swiss canton of Vaud, located in the district of Morges.
Lonay is first mentioned around 1152-60 as Lonna. In 1177 it was mentioned as Losnay.
Lonay has an area, , of . Of this area, or 59.3% is used for agricultural purposes, while or 7.3% is forested. Of the rest of the land, or 32.3% is settled (buildings or roads), or 0.3% is either rivers or lakes and or 0.3% is unproductive land.
Of the built up area, industrial buildings made up 2.2% of the total area while housing and buildings made up 15.4% and transportation infrastructure made up 12.9%. while parks, green belts and sports fields made up 1.1%. Out of the forested land, 5.9% of the total land area is heavily forested and 1.3% is covered with orchards or small clusters of trees. Of the agricultural land, 46.9% is used for growing crops and 1.1% is pastures, while 11.3% is used for orchards or vine crops. All the water in the municipality is flowing water.
The municipality was part of the Morges District until it was dissolved on 31 August 2006, and Lonay became part of the new district of Morges.
It consists of the village of Lonay and the hamlet of Roman.
The blazon of the municipal coat of arms is Or, a Vine eradicated Vert fructed Purpur between two Wheat-heads Vert, in Chief Gules a Cross Argent.
Lonay has a population () of . , 19.9% of the population are resident foreign nationals. Over the last 10 years (1999–2009 ) the population has changed at a rate of 30.7%. It has changed at a rate of 31.6% due to migration and at a rate of -1.1% due to births and deaths.
Most of the population () speaks French (1,609 or 84.7%), with German being second most common (111 or 5.8%) and Italian being third (58 or 3.1%).
Of the population in the municipality 289 or about 15.2% were born in Lonay and lived there in 2000. There were 746 or 39.3% who were born in the same canton, while 369 or 19.4% were born somewhere else in Switzerland, and 444 or 23.4% were born outside of Switzerland.