Mäntsälä (Finnish pronunciation: [ˈmæntsælæ]) is a municipality in the province of Southern Finland, and is part of the Uusimaa region. It has a population of 20,726 (31 March 2016) and covers an area of 596.10 square kilometres (230.16 sq mi) of which 15.26 km (5.89 sq mi) is water. The population density is 35.68 inhabitants per square kilometre (92.4/sq mi).