As of the 2011 Census of India, the city of Sivasagar had a population of approximately 50,781, while the broader Sivasagar district has a population exceeding 1.15 million. The population has grown moderately over the last decade, driven by employment in the energy and tea sectors.
The city boasts a high literacy rate, typically exceeding 84%, which is notably higher than the national average. Assamese is the primary language spoken and understood by the vast majority of residents, followed by Hindi and English.
Demographically, the city is a melting pot of various indigenous communities, prominently including the Ahoms, Assamese Hindus, Assamese Muslims, and the Tea Tribe communities who historically migrated to work in the plantations. Hinduism is the majority religion, with a significant Muslim minority and smaller populations of Christians and Buddhists.
