Kailahun District is a district in the Eastern Province of Sierra Leone. Its capital and largest city is the town of Kailahun. The other major towns in the district include Segbwema, Koindu, Pendembu and Daru. As of the 2015 census, the district had a population of 525,372. Kailahun District is subdivided into fourteen chiefdoms.
The District of Kailahun borders Liberia to the east, Guinea and the Kono District to the north, and Kenema District to the west. The border of the district with Guinea is formed by a section of the Moa River. The total area of the district is 4,859 km2 (1,876 sq mi). The population of Kailahun District is largely from the Mende ethnic group. The district is predominantly muslim.
Kailahun District is the birthplace of former Sierra Leone's president Ahmad Tejan Kabbah, who was born in the town of Pendembu.