Ristijärvi is a municipality of Finland, located in the Kainuu region. It is the smallest municipality in Kainuu by population, with 1,158 residents.
The municipality covers an area of 897.93 square kilometres (346.69 sq mi), of which 62.31 square kilometres (24.06 sq mi) is water. Its population density is 1.39 inhabitants per square kilometre (3.6/sq mi).
Ristijärvi is unilingually Finnish.