Karstula is a municipality of Finland founded in 1867. It is located in the province of Western Finland and is part of the Central Finland region. The municipality has a population of 4,296 (30 June 2015) and covers an area of 963.47 square kilometres (372.00 sq mi) of which 76.22 km (29.43 sq mi) is water. There are all together 159 lakes in Karstula. Biggest lakes are Pääjärvi, Enonjärvi and Vahanka. The population density is 4.84 inhabitants per square kilometre (12.5/sq mi).