Jämsänkoski is a former town and municipality in central Finland located near Lake Päijänne and the Jämsänjoki river. The town had population of 7,351 (2008). It covered an area of 448.67 km² of which 48.02 km² is water. The population density was 16.9 inhabitants per km².
The paper mill owned by UPM Kymmene is the largest employer of Jämsä.
Jämsänkoski was founded in 1926 when it separated from the bigger municipality of Jämsä. Municipality of Koskenpää was consolidated with Jämsänkoski in the beginning of 1969.
It belongs to the administrative district of Western Finland although Central Finland remains the centre for labour and trade. Jämsänkoski was consolidated with Jämsä in 2009.(Wikipedia)