Nousiainen is a Finnish-speaking municipality located in the Southwest Finland region of Finland. It is situated approximately 20 kilometres (12 mi) from the city of Turku along Highway 8 (E8).
The municipality covers a total area of 199.55 square kilometres (77.05 sq mi), which includes 0.62 km2 (0.24 sq mi) of water. As of December 31, 2025, the population is recorded at 4,667 people, resulting in a population density of 23.46 inhabitants per square kilometre (60.8/sq mi).