Kajaani, historically known as Cajanaburg, is a town in Finland and the regional capital of Kainuu. Kajaani is located southeast of Lake Oulu…Kajaani, historically known as Cajanaburg, is a town in Finland and the regional capital of Kainuu. Kajaani is located southeast of Lake Oulu, which drains into the Gulf of Bothnia through the Oulu River. The population of Kajaani is approximately 37,000, while the sub-region has a population of approximately 51,000. It is the 32nd most populous municipality in Finland.