Vellore district is one of the 32 districts in the Tamil Nadu state of India. It is one of the six districts that form Tiruvannamalai region of Tamil Nadu. It is one of the biggest districts in Tamil Nadu. Vellore City is the headquarters of this district. As of 2011, the district had a population of 3,936,331 with a sex ratio of 1,007 females for every 1,000 males.