Nastola is a former municipality of Finland. It was merged with the city of Lahti on 1 January 2016. In the province of Southern Finland, Nastola is part of the Päijät-Häme region. The municipality had a population of 14,905 (30 June 2015) and covered an area of 382.86 km2 (147.82 sq mi) of which 38.67 km2 (14.93 sq mi) was water. The population density was 45.9761/km2 (119.078/sq mi). Nastola is located between two major cities: Lahti and Kouvola. Kausala, the administrative center of Iitti, is 26 kilometres (16 mi) away from Nastola in the direction of Kouvola. The municipality was unilingually Finnish.