Dehradun district (Hindi: [d̪eːɦɾaːd̪uːn] ^ⓘ) is a district in Garhwal division which is a part of Uttarakhand state in northern India. The district headquarters is Dehradun, which has also served as the interim capital of Uttarakhand since its founding in 2000. The district has 6 tehsils, 6 community development blocks, 17 towns, 764 inhabited villages, and 18 unpopulated villages. The district stretches from the Ganges river in the east to the Yamuna river in the west, and from the Terai and Shivaliks in the south and southeast to the Great Himalaya in the northwest. During the British Raj, the official name of the district was Dehra Dun. In 1842, Dun was attached to Saharanpur district and placed under an officer subordinate to the Collector of the district but since 1871 has been administered as a separate district.

Dehradun is located 230 km from the national capital, Delhi. The National Oil and Natural Gas Corporation, Survey of India, and many educational institutions like Doon University, Uttrakhand Technical Institute, Indian Institute of Petroleum, Uttaranchal University, Forest Research Institute, Wildlife Institute of India, Rashtriya Indian Military College and Indian Military Academy are situated here. Basmati rice, tea and litchi orchards are some of the major agricultural crops.

The British seized the region as a war spoil from the Maharaja of Tehri-Garhwal as a consequence of the Gurkha War of 1814–16, and attached it administratively to Saharanpur District to its immediate south, which was already in British hands.

Dehradun includes various Puranic stories and cultures. It is mentioned in the Ramayana that Lord Rama, along with brother Lakshmana, came to the area after defeating Ravana, the Rakshasa king of Lanka. The area is also linked to Dronacharya, the guru of the Kauravas and Pandavas in the Mahabharata. The area of Rishikesh is mentioned in the Skanda Purana as having been given to rishis (sages) by Lord Vishnu after killing the asuras Madhu-Kaitabha and their companions who tormented the rishis. Ancient temples, statues and archaeological remains have been found at the sites in and around the area that are mentioned in the Ramayana and the Mahabharata. These remains have been dated to be approximately 2000 years old.

The location of the area, the ancient traditions and customs still followed here, folk songs coming down from generations, and their contemporaneous literature point to the fact that the area witnessed various events during the periods of the Ramayana and the Mahabharata. The Pandavas held influence over the region after the battle of the Mahabharata and the area was ruled by the descendants of Subahu as administrators under the Kuru kingdom at Hastinapura. The discovery of Ashokan edicts at Kalsi near Dehradun show that the area was quite prosperous. Huen Tsang also observed Kalsi as Sudhanagara in the 7th century AD. Archaeological remains from the time of Raja Rasal have been found at Haripur near Kalsi.

The area was attacked by Mahmud Ghaznavi, Timur in 1368. Guru Ram Rai, the errant eldest son of the seventh Guru of the Sikhs, Guru Har Rai, established his 'Dera' (camp) in the Dun Doon Valley around 1676 and the town that grew around this 'Dera' has come to be known as 'Dehradun'. He founded his own Udasi Panth (sect) and received support from Aurangzeb. Rohilla chieftain Najib ad-Dawlah in 1757 and Ghulam Kadir in 1785. This kept the area in disarray till 1801. The British captured the area in 1816 and founded the cities of Landour and Mussourie in 1827–28. The district was added to the Garhwal division in the 1970s. It was established as the capital of Uttarakhand after the establishment of the state as Uttaranchal in the year 2000.

This State Founded in the mid-15th century by Phoda Singh and Lal Karan Singh, members of the ''Chokker'' family of Hindus, the state remained under the rule of this dynasty until its eventual annexation. In 1548, two prominent Chhokar chieftains, Phoda Singh and Lal Karan, from the Titron region in Saharanpur district, crossed the Sivalik hills, conquered the entire Dehradun area, and established the Timli state. They also founded a town named Timli. Bhagwan Singh was the majestic king of the Chhokar family of Timli. He had the status of a magistrate and he used to fix the prices of agricultural products of north india. When the British Raj entered this area under the Arazi-i-Bandobasti land settlement, they took control of the area around Dehradun, while the rest of the state remained under local rule. By 1830, Bhagwan Singh was the king of Timli state. His only descendant, a daughter named Satyaditi, became the ruler after him.

Raja Ranjit Singh of Samthar state, born in 1943, was married at a young age to a princess from the Chhokar family, which ruled Timli state in Dehradun.