Bongaigaon district (Assamese: [bɒŋaɪgãʊ]) is an administrative district in the state of Assam in northeastern India. The district headquarters are located at Bongaigaon.

According to lore, the name 'Bongaigaon' derives from the words 'bon' (wild) and 'gai' (cow). In the distant past, wild cows were often a menace to villagers in this area due to which the district got its name.

Bongaigaon district fell under Eastern Dooars. Dooars between Sankosh River and Manas River are called Eastern Dooars.

From early 17th-century some parts of present-day Bongaigaon district was under the control of Kingdom of Bhutan, till the Duar Wars in 1865 when British removed the Bhutanese influence and later the areas were merged to undivided Goalpara district of the Indian Union in 1949.

The district was part of Kamrup. In the 14th century, its rule was passed onto the Baro-Bhuyans. Later in the 1580s Nara Narayan of the Kamata kingdom conquered the area and it subsequently became the fiefdom of the Bijni family, who were descendants of Nara Narayan. When the Kamata kingdom split into Koch Bihar and Koch Hajo due to rivalry between the king and his nephew Raghu Rai, Bongaigaon became part of Koch Hajo. Soon Koch Hajo and Koch Bihar went to war, and the Mughal Nawab of Dhaka, supporting Koch Bihar, defeated Rai at Dhubri in 1602. Rai's son Parikshit signed a peace treaty, but hostilities resumed in 1614 and Parikshit was driven back to modern-day Guwahati, where he surrendered and soon after died. His son, Bijit Narayan, was made Zamindar of the region between the Manas and Sankosh: from him the Bijni family descended. Koch Hajo was tributary to the Mughals, but in the last decades of the 17th century Mughal influence waned significantly due to the Ahom-Mughal wars in which the Ahoms were eventually successful. Koch Hajo, including Bijni Zamindari, fell under Ahom influence.

The district of Bongaigaon was created on 29 September 1989 from parts of Goalpara and Kokrajhar districts. 2004 saw a loss of size when part of the district was split to make Chirang district.

In the late 1750s, the East India Company strengthened their influence in Bengal and Lower Assam. In 1822 the East India Company created Goalpara district containing present-day Lower Assam, the Garo Hills and northeastern Rangpur division in Bangladesh. The Bijnis continued to pay tribute to the British, and even gained a small amount of land after the Duar War in 1865. Rangpur and the Garo Hills were eventually stripped away to form different districts, but Goalpara continued to be administered as part of a Cooch Behar province. Eventually the Assam Valley province was founded in 1874, and Goalpara was moved to it. Goalpara was later divided into various districts including Kokrajhar and Dhubri, and later Bongaigaon.

Bongaigaon district occupies an area of 1,093 square kilometres (422 sq mi), comparatively equivalent to Réunion. Bongaigaon district is surrounded by Barpeta in the east, the Brahmaputra in the south and Kokrajhar in the north and west corner and share international border with Bhutan in the north.