Marttila (Finnish: [ˈmɑrtːilɑ]; Swedish: S:t Mårtens, i.e. "Saint Martin's") is a municipality of Finland. It is located in the province of Western Finland and is part of the Southwest Finland region. The municipality has a population of 1,924 (31 August 2024) and covers an area of 195.99 square kilometres (75.67 sq mi) of which 0.71 km2 (0.27 sq mi) is water. The population density is 9.85 inhabitants per square kilometre (25.5/sq mi).
The municipality is unilingually Finnish.
Marttila's neighbouring municipalities are Koski Tl, Lieto, Loimaa, Paimio, Pöytyä and Salo.
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