Ypäjä is a municipality located in the countryside of South-Western Finland. It belongs to the province of Southern Finland and the region of Tavastia Proper. The municipality has a population of 2,458 (30 June 2015) 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 13.45 inhabitants per square kilometre (34.8/sq mi). The municipality is unilingually Finnish.
The main population centre of Ypäjä is a small village situated on the river Loimijoki, between the towns of Forssa (23 km to the east from Ypäjä) and Loimaa (15 km to the west). Although officially part of the Forssa region, Ypäjä is often also considered to belong to the Loimaa region as it has traditionally been influenced by both towns. Besides Loimaa, its direct neighbours are Jokioinen, Humppila, Somero, Koski, and Mellilä.
The distances from Ypäjä to the three major cities in southern Finland are relatively short: 74 kilometres (46 mi) to Turku, 96 km (60 mi) to Tampere, and 132 km (82 mi) to the capital Helsinki.