Montmagny is a former municipality in the district of Broye-Vully in the canton of Vaud in Switzerland.
The municipalities of Bellerive, Chabrey, Constantine, Montmagny, Mur, Vallamand and Villars-le-Grand merged on 1 July 2011 into the new municipality of Vully-les-Lacs.
Montmagny is first mentioned in the 13th Century as Manniaco. In 1458 it was mentioned as Montmagniel.
Montmagny has an area, , of . Of this area, or 72.9% is used for agricultural purposes, while or 21.3% is forested. Of the rest of the land, or 4.5% is settled (buildings or roads), or 1.8% is either rivers or lakes.
Of the built up area, housing and buildings made up 3.2% and transportation infrastructure made up 1.3%. Out of the forested land, 19.2% of the total land area is heavily forested and 2.1% is covered with orchards or small clusters of trees. Of the agricultural land, 67.9% is used for growing crops and 2.9% is pastures, while 2.1% is used for orchards or vine crops. All the water in the municipality is flowing water.
The municipality was part of the Avenches District until it was dissolved on 31 August 2006, and Montmagny became part of the new district of Broye-Vully.
The municipality is located in the hill country of the Vully region.
The blazon of the municipal coat of arms is Or, on a Coupeaux Vert a Wolf rampant Sable langued Gules.
Montmagny has a population () of 180. , 7.8% of the population are resident foreign nationals. Over the last 10 years (1999–2009 ) the population has changed at a rate of 8.4%. It has changed at a rate of 12.7% due to migration and at a rate of -1.8% due to births and deaths.
Most of the population () speaks French (126 or 80.8%), with German being second most common (20 or 12.8%) and Portuguese being third (4 or 2.6%). There are 3 people who speak Italian.
Of the population in the municipality 64 or about 41.0% were born in Montmagny and lived there in 2000. There were 13 or 8.3% who were born in the same canton, while 60 or 38.5% were born somewhere else in Switzerland, and 14 or 9.