Dera Ismail Khan District (Urdu and Saraiki: ضلع ڈیره اسماعیل خان, Pashto: دېره اسماعيل خان ولسوالۍ), often abbreviated as D.I. Khan is a district in the Dera Ismail Khan division of the Khyber Pakhtunkhwa province of Pakistan. The capital of the district is the town of Dera Ismail Khan. The district has an area of 9,334 km² (3,604 sq mi) and a population of 1,822,916 as of the 2023 Census. After the Second Anglo-Sikh war in 1849 the district was annexed by the British as part of the Punjab and remained so until 1901 when the North West Frontier Province or NWFP (now renamed as Khyber Pakhtunkhwa) was created.

The district of Dera Ismail Khan is bounded on the North east by the Bhakkar and Dera Ghazi Khan districts of Punjab. Eastern portions of the district along the Indus river are characterized by fertile alluvial plains, while lands farther from the river consist of clay soil cut by ravines from rainfall. The district is bounded on the southwest by a thin strip of the South Waziristan district, which separates D.I Khan from the Koh-e-Sulaiman mountain in the neighboring Baluchistan province. In the northwest is the Tank District.

D.I Khan is separated from the Marwat plains of the Lakki Marwat district by a spur of clay and sandstone hills that stretch east from the Sulaiman mountains to the Indus river known as the Sheikh Badin Hills.^{[citation needed]}

The highest peak in the range is the limestone Sheik Badin mountain, which is protected by the Sheikh Badin National Park. Near the Indus River is a spur of limestone hills known as the Kafir Kot hills, where the ancient Hindu complex of Kafir Kot is located. DI Khan is also considered the center of Pakistan because of its location between Bhakkar, Mianwali of North Punjab, Zhob of Balochistan and South Waziristan of Pakistan's tribal belt.^{[citation needed]}

It is named after Dodai mercenary Ismail Khan, son of Malik Sohrab Dodai of the Langah Sultanate, who laid the foundation of the area.

The Dera Ismail Khan District is littered with ruins from ancient civilizations. Dera Ismail Khan is home to the collection of Hindu ruins from two separate sites 20 miles apart, jointly known as Kafir Kot.

The region came under the influence of the Nanda empire of the ancient India from 300 BCE. With the rise of Chandragupta Maurya, the region came under the complete control of the Mauryan empire. Afterward, the region was briefly and nominally controlled by the Shunga empire. However, with the decline of the Shungas, the region passed to local Hindu and Buddhist rulers and was interrupted by foreign rulers. Many of these foreign rulers, like the Indo-Parthians, Sakas, and Kushans converted to Hinduism and Buddhism and promoted these Indian religions throughout central and south Asia. The region reached its height under the Buddhist ruler Kanishka. After the fall of the Kushans, the region came under the control of the Gupta empire of the ancient India. During this period, Hindu and Buddhist art and architecture flourished in the area.

With the decline of the imperial Guptas, the Hindu Shahis came to rule the area. The Hindu Shahis built two massive forts in the northern edges of Dera Ismail Khan. The forts were later renamed as "Kafir kots" (forts of the Kuffar (Disbelievers)). These Hindu Shahi forts were known for high towers and steep defensive walls. The Hindus also built many Hindu temples around the area. However, many of them are now in rubble. The Hindu Shahis remained in control of the area until their defeat by the Turkic Muslim army of Ghaznavids.