Karstula is a municipality in Finland, located in the Central Finland region. It was founded in 1867.
The municipality has a population of 3,514 and covers an area of 963.19 square kilometres (371.89 sq mi), of which 76.22 square kilometres (29.43 sq mi) is water. Its population density is 3.96 inhabitants per square kilometre (10.3/sq mi).