The Indian Census is the largest source of statistical information about the population and has been conducted every 10 years since 1872, with the last census in 2011. It involves a two-phase process: house listing and population enumeration, covering all states and union territories. Key findings from the 2011 census include a population of over 1.2 billion, a literacy rate of 74%, and a sex ratio improvement from 933 to 943 females per 1000 males since 2001.