Dima Hasao district — earlier called North Cachar Hills district is an administrative district in the state of Assam in north-eastern India. As of 2011 it is the least populous district of Assam (out of 27). “Dima Hasao” means “Dimasa Hills” in the Dimasa language.

Dima Hasao District district was a part of Dimasa Kachari Kingdom before 1832. The kingdom was extended from Jamuna in the North to the foot-hills of Lushai Hills in the south and from the Kopili in the west to the Angami and Katcha Naga hills beyond the Dhansiri in the east. The Dimasa Kachari kings had their capitals successively at Dimapur, Maibang, Kashpur, and, lastly, at Horitikor (Karimganj district near Badarpur). In 1830, the Dimasa king Gobinda Chandra Hasnu was assassinated by his own general Gambhir Singh, after that the British annexed the southern part of the kingdom on 14 August 1832 under the doctrine of Lapsi. The rest was ruled by last Dimasa General Tularam. In 1837, a portion of Tularam’s kingdom was further annexed to the British Empire and constituted into a sub-division of Nagaon district in 1837 with Headquarter at Asalu. In 1854, on the death of Tularam, the remaining portion of his kingdom was finally annexed to the British Empire and added to the Asalu sub-division.

In 1867, this sub-division was abolished and apportioned into three parts among the districts Cachar, Khasi and Jaintia Hills, and Nagaon.

The present North Cachar Hills district was included in the old Cachar district with Asalu being only police outpost. In 1880, this portion was constituted into a sub-division with headquarters at Gunjung under Cachar district.

This headquarters was shifted to Haflong in 1895. Since then, Haflong continues to be the headquarters. In 1951, after commencement of the constitution of India, North Cachar Hills as specified under paragraph 20 of the sixth schedule to the constitution, ceased to be a part of Cachar district. This part along with Mikir Hills constituted a new civil district namely “United district of North Cachar and Mikir Hills”, which when into effect on 17 November 1951. According to the provision of sixth schedule, two different councils were constituted later on, viz., North Cachar Hills District Council and Mikir Hills District Council within the geographical boundary of that district. Dima Hasao District District Council was inaugurated on 19 April 1952.

On 2 February 1970, the government declared an independent administrative district, viz., North Cachar Hills District with the geographical boundary of autonomous North Cachar Hills district council. At present, this autonomous council possesses administrative control over almost all departments of the district except law and order, administration, and the treasury Department.

In 2006 the Indian government named Dima Hasao one of the country’s 250 most backward districts (out of a total of 640). It is one of the eleven districts in Assam currently receiving funds from the Backward Regions Grant Fund Programme.

According to the 2011 census Dima Hasao district has a population of 213,529, roughly equal to the nation of Samoa. This gives it a ranking of 588th in India (out of a total of 640). The district has a population density of 44 inhabitants per square kilometre (110/sq mi) .Its population growth rate over the decade 2001-2011 was 13.53%. Dima Hasao has a sex ratio of 931 females for every 1000 males, and a literacy rate of 78.99%.

The major tribes inhabiting the district are Dimasas, Zeme Nagas, Biate, Hmars, Kukis, Hrangkhawls, Vaipheis, Karbis, Khasi-pnars and Khelmas.

Major languages spoken in the district are the Bengali, Assamese, Dimasa, Hmar, Karbi, Khelma, Kachari, Zeme, Hrangkhol, Kuki, Biate [Biate language], and few languages of Indo-Aryan like Haflong Hindi (a speech form of Hindi), Nepali Haflong Hindi is the lingua franca in the Dima Hasao.