The name of the district is derived from a story found in Hindu epics specifically the Bhagavata Purana and in the locally composed Kalika Purana by the Brahmin pandits where the city was established by Banasura the eldest son of Bali who did great penance or tapasya to Lord Shiva who promised to look over the city.

[1] The Koriapar Dooar falls under the Sonitpur district and was held by Bhutias known as the Monpas (Tibetan: མོན་པ་) and to the Chinese as Monbas.

[3] The Koriapar Dooars was annexed by British East India Company in 1844 and added to the Assam province.

Koch Hajo's boundary with the Ahoms was at the Kameng river, also known as the Bareli, which flowed through the middle of what is now Sonitpur district.

However the rains that set in during their retreat, as well as the diseases, took a huge toll on the Mughal army, and the Ahoms soon took back Guwahati and kept it.

The British introduced tea plantation to the district, and imported large numbers of labourers from the tribal belt of Chota Nagpur to the Sonitpur area.

[5] Sonitpur district lies on the plains between the foothills of the Himalayas and the valley of the Brahmaputra which forms its southern border.

[9] Other than the Brahmaputra, the major rivers in the district are its right tributaries and include the Jiabharali, Gabharu, Borgang and Buroi.

In 1998, Sonitpur district became home to Nameri National Park in the north, which has an area of 200 km2 (77.2 sq mi).

Rainfall is heavy above 3,000 mm (9 ft) in wet months January to June which is both a boon and a bane for the people.

[7] Species include: Aegle marmelos, Albizia procera, Alstonia scholaris, Arundo donax, Bambusa balcooa, Cynodon dactylon, Dipterocarpus macrocarpus, Duabanga grandiflora, Eichhornia crassipes, Mesua assamica, Melocanna baccifera, Mesua ferrea, Shorea assamica (mekai) and Shorea robusta.

According to the 2011 census Sonitpur district has a population of 1,924,110,[13] roughly equal to the nation of Lesotho[14] or the US state of West Virginia.

These are Assamese Brahmins, Koch Rajbongshis, Ahom, Karbi, Keot (Kaibarta), Mising, Nath Jogis, Bodo, Thengal Kachari, Chutia, Rabha, Gorkhas and other communities of Assam.

They have become a minority in the district due to the colonial and post-colonial era settlement of communities like Bengalis (both Hindu and Muslim), Biharis, Marwaris etc.

[17] The immigrant Bengali speaking Hindus came from erstwhile undivided Bengal and Bangladesh, as officials and clerks of the British administration and the Tea Industry; and stayed back.

Later, on account of the partition of India, Hindu people from Bangladesh coming as refugees added significantly to the community.

They are mostly urbanised having a sizeable population in towns of Rangapara, Tezpur, Dhekiajuli, Biswanath Chariali, and Balipara.

Their ancestors were brought from tribal areas of central India to work as labourers on tea plantations.

However, they are mostly concentrated in the surrounding regions of Dhekiajuli, Rangapara, Balipara, Jamugurihat, Biswanath chariali, Behali, Gohpur, Helem and northern parts of the district.

As per the 2011 census, 37.01% of the population spoke Assamese, 19.36% Bengali, 12.52% Sadri, 8.93% Boro, 6.63% Nepali, 3.79% Hindi, 2.54% Odia and 1.98% Mundari as their first language.