Decennial population census

Also called: Census of India, Population census · Topic: Economic Data: Census, NSS, Surveys and Statistical Tools · NCERT: Class 11, Ch 2 "Collection of Data"; Class 11, Ch 3 "Organisation of Data"; Class 11, Ch 4 "Presentation of Data"

Meaning

The decennial population census (Census of India) is a complete count of every person in India, held once every ten years. Everyone is counted with reference to the same date and hour. It has been held without a break since the first synchronous census of 1881. Census 2011 was the 15th, and Census 2027 will be the 16th, with its reference date at 00:00 hrs on 1 March 2027 [2][4].

It matters because the census is India's master list of people, households and villages. Surveys like NSS and PLFS draw their samples from it. Seat allocation in legislatures and welfare coverage such as NFSA also rest on its figures.

Key census formula:

• Decadal growth rate (%) = (Population in census year − Population ten years earlier) ÷ Population ten years earlier × 100

Explanation

How a census works

• Census method: every unit (every person and every household) is counted. Nobody is sampled.
• Sample survey (for example NSS or PLFS): only a small, carefully chosen part is studied. That part is then used to estimate the whole.
• Why only once in ten years: a census is costly and slow. Sample surveys fill the gap between two censuses.
• Synchronous census: the whole country is counted with reference to the same date and hour. This is called the reference date.
• People move during the counting period.
• If there were no common moment, a migrant could be counted twice, or missed.

• A single reference moment stops both errors.

• Two phases:

• Phase I, Houselisting and Housing Census (HLO): data on each building and house. It covers housing condition and amenities such as drinking water, toilet, electricity, cooking fuel and assets.
• Phase II, Population Enumeration (PE): data on each person. It covers age, sex, literacy, work, migration, fertility and more.

What the census measures

• Density (how crowded an area is) = Population ÷ Area (km²).
• Sex ratio (in India, females per 1,000 males) = (Females ÷ Males) × 1,000.
• Literacy rate = Literates ÷ Population aged 7+ × 100.

• A person aged 7 or above who can read and write, with understanding, in any language counts as literate.

• Workers:

• Main worker: worked 6 months (183 days) or more in the year before the census.

• Marginal worker: worked for less than 6 months.

• Migration: place of birth and last place of residence.

• Rural-urban split, plus birth and death rates and life expectancy, including fertility questions.

Worked example 1: decadal growth, Census 2011

• Population in 2001 = 102.87 crore. Population in 2011 = 121.09 crore.
• Growth = (121.09 − 102.87) ÷ 102.87 × 100
• = 18.22 ÷ 102.87 × 100 ≈ 17.7%

Worked example 2: sex ratio, Census 2011

• There were about 58.75 crore females and 62.33 crore males.
• Sex ratio = 58.75 ÷ 62.33 × 1,000 ≈ 943

Worked example 3: density (toy numbers)

• A district has 20 lakh people on 5,000 km².
• Density = 20,00,000 ÷ 5,000 = 400 persons/km²

History: from 1872 to the 2027 round

• 1872: the first count, under Lord Mayo. It was non-synchronous, meaning different regions were counted at different times.
• 1881: the first synchronous census, under Census Commissioner W.C. Plowden. The census has been decennial (every ten years) since then.
• 1951: the first census after Independence.
• 2011: the 15th census overall and the 7th after Independence.
• 2021: the round was postponed because of COVID and became Census 2027.

• This is the first time the census missed its ten-year slot since 1881.

• Census 2027: the 16th census and the 8th since Independence [4].

How the population series has moved (NCERT, crore)

1901	1951	1961	1971	1981	1991	2001	2011
23.83	35.7	43.8	54.6	68.4	81.8	102.7	121.0

• NCERT rounds these figures. The exact numbers are 102.87 crore for 2001 and 121.09 crore for 2011.
• The population grew by over 97 crore in 110 years (1901–2011).
• 1921, the "Year of Great Divide":
• Before 1921, population rose and fell with famines and epidemics.

• After 1921, it rose every decade.

• Average annual growth rate (the yearly compound rate that produces the decade's rise) is falling:

• 2.2% in 1971–81 → 1.97% in 1991–2001 → 1.64% in 2001–11.
• This shows demographic transition, the move from high birth and death rates to low ones.

In India

• Law: the Census Act 1948.
• Answering the census is compulsory.

• Each person's answers stay confidential. Only totals are published.

• Constitution: the census is Entry 69 of the Union List (Seventh Schedule). Only Parliament can make laws on it.

• Institution: the Office of the Registrar General & Census Commissioner, India (ORGI), set up in 1949 under the Ministry of Home Affairs. One officer holds both posts.
• Census 2011 figures:
• Population: 121.09 crore (final). The first provisional release put it at "1,210 million" [6].
• Sex ratio: 943. Rural 949, urban 929 [7]. Females were about 48.5% of the population [7].
• Literacy: 74.04%, up from 64.83% in 2001, a rise of 9.21 percentage points [6][7]. Female literacy rose from 53.7% to 65.5%, but it still lagged male literacy.
• Density: 382 persons/km² [8].

• Decadal growth: 17.64%, the lowest since Independence. Males 17.19%, females 18.12% [8].

• Census 2027:

• Notified in June 2025. It runs in two phases, along with caste enumeration [3].
• The Cabinet approved it at a cost of ₹11,718.24 crore, with about 30 lakh field functionaries [2].
• Reference date: 00:00 hrs, 1 March 2027. For Ladakh and the snow-bound, non-synchronous areas of J&K, Himachal Pradesh and Uttarakhand, it is 00:00 hrs, 1 October 2026 [2].
• Phase I (HLO), April–September 2026: each State or UT picks a 30-day window, preceded by an optional 15-day self-enumeration period [4]. The first states to start HLO were Andhra Pradesh, Arunachal Pradesh, Haryana, Chandigarh, Madhya Pradesh and Chhattisgarh [5].
• Phase II (PE), February 2027: demographic, socio-economic, cultural, migration and fertility details [4]. In snow-bound areas, PE is held in September 2026 [2].
• First digital census: data are collected on mobile apps, and households can fill in their own details on a Self-Enumeration Portal [4].

• First caste enumeration since 1931: the CCPA decided this on 30 April 2025. Until 2011, only SCs and STs were counted [4].

• Other RGI data systems: the SRS and the CRS (under the RBD Act 1969). The RBD (Amendment) Act 2023 requires the Registrar General to keep a national database of births and deaths and makes the birth certificate a single document to prove date and place of birth [9].

Don't confuse with

• Sample survey (NSS, PLFS): it covers only a chosen sample and runs often. The census counts everyone, once in ten years. The census also provides the sampling frame (master list) that these surveys use.
• SECC 2011 (Socio-Economic and Caste Census): a separate exercise, not a census under the Census Act 1948. Its caste data are unreleased. Census 2027 is the first census to count all castes since 1931 [4].
• SRS (Sample Registration System): a continuous sample survey. It gives yearly IMR, TFR and MMR, which the ten-yearly census cannot give. It is run by the same RGI.
• CRS and NPR: the CRS is the ongoing, compulsory registration of births and deaths under the RBD Act 1969. The NPR is a register of usual residents. Neither is a headcount at one fixed moment.

Prelims Hooks

• 1872 (Lord Mayo) = non-synchronous. 1881 (W.C. Plowden) = first synchronous census, decennial ever since. 1951 = first census after Independence.
• Census = Entry 69, Union List. Law = Census Act 1948. Office = ORGI, under MHA (1949). Trap: "Census of India" and "RGI" are one office, not two.
• Census 2027 = 16th census, 8th after Independence. Reference date 1 March 2027, 00:00 hrs, but 1 October 2026 for snow-bound areas [2][4].
• Census 2027 costs ₹11,718.24 crore and uses about 30 lakh field functionaries [2]. Caste enumeration was approved by the CCPA on 30 April 2025, the first since 1931 [4].
• Census 2011: sex ratio 943 (rural 949, urban 929), literacy 74.04%, density 382/km², decadal growth 17.64% [7][8].
• Literacy counts only people aged 7+. A main worker worked 183 days or more. A marginal worker worked less than 6 months.

Mains Points

• Data gap weakens policy (GS-III):
• The gap from 2011 to 2027 is 16 years. NSS and PLFS frames, per-capita figures and NFSA coverage (75% rural, 50% urban) all still rest on 2011 numbers.
• The population has grown since then, so people who should be eligible may be left out and survey estimates may be biased.

• A timely census is basic public infrastructure for evidence-based planning.

• Census 2027 links delimitation, women's reservation and federalism (GS-II):

• Articles 82 and 170 freeze seat allocation until the first census after 2026, and Census 2027 is that census.
• The new count may shift seats between states. States that slowed their population growth, mostly in the south, fear they will lose relative weight.

• Art 334A (106th Amendment, 2023) gives women one-third of seats only after this census and the delimitation based on it.

• Caste count and digital census: gains vs risks:

• Gains: evidence for reservation, sub-categorisation and welfare targeting. Apps and self-enumeration give faster results with fewer errors [4].
• Risks: thousands of self-reported caste names are hard to classify, the data can be politicised (SECC 2011's caste data were never released), and there are concerns about the digital divide and privacy.
• Linking census data with the NPR and the RBD database must not weaken the confidentiality promised by the Census Act 1948.

Related concepts

• Demographic data

Read more

• The Census of India: 1881 to the 2027 round