India has added 181 million new people to its population over the last decade, according to the results of the 2011 census.
India's population is now 1.21bn, which is bigger than the combined populations of the US, Indonesia, Brazil, Pakistan and Bangladesh.
India launched the latest census exercise last year.
Some 2.5 million officials visited households in about 7,000 towns and 600,000 villages.
The population was classified according to gender, religion, education and occupation.
The exercise, conducted every 10 years, faces big challenges, not least India's vast area and diversity of cultures.
Census officials also have to contend with high levels of illiteracy and millions of homeless people - as well as insurgencies by Maoists and other rebels which have left large parts of the country unsafe.