As of the 2011 Census, the municipal area of Bongaigaon had a population of approximately 67,322, though the broader urban agglomeration—including the railway and refinery townships—exceeds 100,000 residents. The city has seen steady population growth driven by industrial employment and rural-to-urban migration.
Bongaigaon boasts a highly diverse and cosmopolitan demographic. The ethnic composition includes Assamese, Bodos, Bengalis, and significant communities of Hindi-speaking business families (Marwaris) and railway/refinery workers from across India. Hinduism is the majority religion, followed by Islam, Christianity, Jainism, and Sikhism. The city is known for a high literacy rate of over 85%, significantly outperforming both state and national averages.