<Tr> <Th> Least populous state </Th> <Td> Sikkim (610,577) </Td> </Tr> <P> The 15th Indian Census was conducted in two phases, house listing and population enumeration . House listing phase began on 1 April 2010 and involved collection of information about all buildings . Information for National Population Register was also collected in the first phase, which will be used to issue a 12 - digit unique identification number to all registered Indian residents by Unique Identification Authority of India (UIDAI). The second population enumeration phase was conducted between 9 and 28 February 2011 . Census has been conducted in India since 1872 and 2011 marks the first time biometric information was collected . According to the provisional reports released on 31 March 2011, the Indian population increased to 121 crore with a decadal growth of 17.64% . Adult literacy rate increased to 74.04% with a decadal growth of 9.21% . The motto of census 2011 was' Our Census, Our future' . </P> <P> Spread across 29 states and 7 union territories, the census covered 640 districts, 5,767 tehsils, 7,933 towns and more than 6 lakh villages . A total of 27 lakh officials visited households in 7,933 towns and 6 lakh villages, classifying the population according to gender, religion, education and occupation . The cost of the exercise was approximately ₹ 2,200 crore (US $340 million)--this comes to less than $0.50 per person, well below the estimated world average of $4.60 per person . Conducted every 10 years, this census faced big challenges considering India's vast area and diversity of cultures and opposition from the manpower involved . </P> <P> Information on castes was included in the census following demands from several ruling coalition leaders including Lalu Prasad Yadav, Sharad Yadav and SP suprimo Mulayam Singh Yadav supported by opposition parties Bharatiya Janata Party, Akali Dal, Shiv Sena and Anna Dravida Munnetra Kazhagam . Information on caste was last collected during the British Raj in 1931 . During the early census, people often exaggerated their caste status to garner social status and it is expected that people downgrade it now in the expectation of gaining government benefits . There was speculation that there would be a caste - based census conduced in 2011, the first time for 80 years (last was in 1931), to find the exact population of the "Other Backward Classes" (OBCs) in India . This was later accepted and the Socio Economic and Caste Census 2011 was conducted whose first findings were revealed on 3 July 2015 by Union Finance Minister Arun Jaitley . Mandal Commission report of 1980 quoted OBC population at 52%, though National Sample Survey Organisation (NSSO) survey of 2006 quoted OBC population at 41% </P>

Number of villages in india as per 2011 census