Jämsä is a town and municipality in Finland, located in the Central Finland region. It lies about 58 kilometres (36 mi) southwest of Jyväskylä, the region's largest city.
With a population of 19,020, Jämsä is the second most populous town in Central Finland after Jyväskylä. The municipality covers a total area of 1,823.90 square kilometres (704.21 sq mi), of which 252.57 square kilometres (97.52 sq mi) is water. Its population density is 12.1 inhabitants per square kilometre (31 per square mile).