From the Wikipedia page 
Kasulu Town is the second largest town in Kigoma Region, the first one being Kigoma-Ujiji municipality, also the thirteenth most populous town in Tanzania with a population of 208,244 as of 2012.
Kasulu is located in northwestern Tanzania, near the international border with the Republic of Burundi. The town lies at the centre of Kasulu District, Kigoma Region. It is located approximately 78 kilometres (48 mi), by road, northeast of Kigoma, the location of the regional headquarters. Kasulu lies approximately 800 kilometres (500 mi), by road, northwest of Dodoma, the capital of Tanzania.