Ypäjä is a municipality in the countryside of south-western Finland, belonging to the region of Kanta-Häme. It is a rural, unilingually Finnish municipality.
The municipality has a population of 2,186 (31 December 2025) and covers an area of 183.25 square kilometres (70.75 sq mi), of which 0.5 km2 (0.19 sq mi) is water. The population density is 11.96 inhabitants per square kilometre (31.0/sq mi).