According to the 2011 Census of India, the city proper of Itanagar had a population of approximately 59,490, while the larger Capital Complex (including Naharlagun and Nirjuli) had a population of around 122,930. The population has grown significantly over the last decade due to urbanization and the centralization of government services.
The demographic composition is highly diverse. The Nyishi tribe is the largest indigenous group in the city, but Itanagar is a melting pot of almost all major Arunachali tribes, including the Adi, Apatani, Monpa, and Galo. Additionally, there is a substantial population of migrants from other Indian states (such as Assam, Bihar, and West Bengal) who work in government, commerce, and construction.
Religiously, the population is mixed. Christianity is widely practiced among the tribal populations. The indigenous Donyi-Polo faith (animistic worship of the Sun and Moon) remains deeply culturally significant. Hinduism is also widely practiced, predominantly by non-tribal residents and some indigenous groups, alongside a visible Buddhist minority. The literacy rate in the city is high, exceeding 82%, well above the state average.