The 1951 Census of India was the 9th in a series of censuses held in India every decade since 1871. It is also the first census after independence and Partition of India. 1951 census was also the first census to be conducted under 1948 Census of India Act.
The population of India was counted as 361,088,090 (1:0.946 male:female) Total population increased by 42,427,510, 13.31% more than the 318,660,580 people counted during the 1941 census. No census was done for Jammu and Kashmir in 1951 and its figures were interpolated from 1941 and 1961 state census. National Register of Citizens of India (NRC) was prepared soon after the census.
1951 Census of India Wikipedia
Separate figures for Hindi, Urdu, and Punjabi were not issued, due to the fact the returns were intentionally recorded incorrect in states such as East Punjab, Himachal Pradesh, Delhi, PEPSU, and Bilaspur.
Hindus comprises 303.6 million(84.1%) and Muslims were 35.4 million(9.8%) in 1951 census. 1951 Indian census showed that there were 8.3 million Christians. Hindus comprised about 66 per cent of the population of India before partition.Population trends for major religious groups in India (1951)