Dera Ismail Khan (Urdu: ضلع دېره اسماعیل خان) is one of the 26 districts in the Khyber Pakhtunkhwa province of Pakistan. The capital of the district is the town of Dera Ismail Khan. The district has an area of 7,326 km2 (2,829 sq mi) and a population of 852,995 as of the 1998 Census.
Dera Ismail Khan was created as an administrative unit of British India, part of the Derajat Division of the North-West Frontier Province, though this was not accepted by the local rulers. It was formerly divided into two almost equal portions by the Indus River, which intersected it from north to south. To the west of the Indus the characteristics of the country resembled those of Dera Ghazi Khan. This region included lar, home of the BALOCHS of lar. To the east of the present bed of the river there is a wide tract known as the Kachi, exposed to river action. Beyond this, the country rises abruptly, and a barren, almost desert plain stretches eastwards, sparsely cultivated, and inhabited by nomadic tribes of herdsmen. In 1901 the trans-Indus tract was allotted to the newly formed North-West Frontier Province, the cis-Indus tract remaining in the Punjab jurisdiction. The cis-Indus portions of the Dera Ismail Khan and Bannu districts now comprise the new Punjab district of Mianwali. Wheat and wool were exported. In 1901 it contained an area of 8,814 km2 (3,403 sq mi) and a population of 252,379, claimed to be 'chiefly' Baluch Muslims and other Muslims though there is dispute about the truth in this because it is a Pashtun territory. In 1947 it became part of the newly independent Pakistan(By Nisar Chishti). The predominantly Muslim population supported Muslim League and Pakistan Movement. After the independence of Pakistan in 1947, the minority Hindus and Sikhs migrated to India while the Muslim refugees from India settled in the Dera Ismail Khan District.
Saraiki dialect of Punjabi is the mainly spoken in DI khan as well neighboring Tank district. Pashto is also spoken by migrants from Waziristan settled in the district. The local residents of Dera Ismail Khan are called "Dera Waal". The vast majority of people are conversant in Urdu, while English is understood by the educated.