Iitti is a municipality of Finland. It is located in the province of Southern Finland and is part of the Päijät-Häme region. The municipality has a population of 6,329 and covers an area of 687.09 square kilometres (265.29 sq mi) of which 97.27 km2 (37.56 sq mi) is water. The population density is 10.73 inhabitants per square kilometre (27.8/sq mi). Neighbour municipalities are Heinola, Kouvola, Lapinjärvi, Lahti and Orimattila. The municipality is unilingually Finnish.