Bonthe District is a district comprises several islands and mainland of the Atlantic Ocean in the Southern Province of Sierra Leone. Its capital is the town of Mattru Jong and its largest city is Bonthe, on Sherbro Island. As of the 2015 census, the district had a population of 200,730.The district is the least populous in Sierra Leone. Bonthe District is subdivided into eleven chiefdoms.
The District occupies a total area of 3,468 km². The District of Bonthe borders the Atlantic Ocean to the west, Moyamba District to the northwest, Bo District to the southeast and Pujehun District to the south.
Bonthe district is primarily inhabited by the Sherbro people (who are the native people of the district); and the Mende people, who immigrated to the district from Mende-dominant areas in the southern part of Sierra Leone.
Bonthe District has one of the world's largest deposits of titanium ore (rutile) in the world. Sierra Rutile Limited, owned by a consortium of US and European investors, began commercial mining operations in Bonthe in early 1979. Due to poor mining policy, the region has little to show for this huge economic potential. There are no good roads, water supply or electricity. Bonthe District continues to suffer from one of the worst environmental degradation episodes in living memory.