Iitti (Swedish: Itis) is a municipality of Finland.
It is located in the province of Southern Finland and is part of the Kymenlaakso region. The municipality has a population of 6,948 (30 June 2015) and covers an area of 687.08 square kilometres (265.28 sq mi) of which 97.27 km2 (37.56 sq mi) is water. The population density is 11.78 inhabitants per square kilometre (30.5/sq mi).
Neighbour municipalities are Heinola, Kouvola, Lapinjärvi, Nastola and Orimattila.
In 1990, the center of Iitti, which surrounds the old parish church, was voted the most attractive kirkonkylä ("church village") in Finland.
The municipality is unilingually Finnish.
Anttila, Haapakimola, Haapalahti, Isokylä, Jokue, Kalaksue, Kauramaa, Kausala (Kausansaari), Kirkonkylä, Koliseva, Konttila, Koskenniska, Kukonoja, Kuukso, Kuusanniemi, Kymentaka (Kymentausta), Kyrönkylä, Kyöperilä, Leppäniemi, Lyöttilä, Mankala, Maunuksela, Muikkula, Munakallio, Niinimäki, Nirvinen, Parikka, Perheniemi, Piilahti, Puolakka, Pyörylä, Radansuu, Ruokoniemi, Saaranen, Savijoki, Siikakoski, Sitikkala, Säkkilänmaa, Säyhtee, Sääskjärvi, Taasia, Tapola, Tillola, Vuolenkoski and Väärtti.