Iitti 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 and covers an area of of which is water. The population density is .
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.