Tohmajärvi is a municipality of Finland. It is located in the North Karelia region. The municipality has a population of 3,999 (31 August 2024) and covers an area of 895.36 square kilometres (345.70 sq mi) of which 57.62 km2 (22.25 sq mi) is water. The population density is 4.77 inhabitants per square kilometre (12.4/sq mi). The municipality is unilingually Finnish.