Bongaigaon is a city and the administrative headquarters and municipal board of Bongaigaon District, Assam, India.It is considered to be the sixth largest city of Assam .The city, divided into two parts - Old Bongaigaon and New Bongaigaon, is situated 180 kilometres (112 mi) north west of Guwahati. To meet the demands of Bodos of Assam, Bongaigaon was recently carved up to give way for Chirang district. Bongaigaon has a major petrochemical industry, the Indian Oil Corporation Limited (IOCL BGR).