NEW DELHI — India began the first phase of the world's largest national population count on Wednesday, launching a census originally planned for 2021 but postponed due to the COVID-19 pandemic and logistical challenges. The initial phase will run through September across the country, with census workers spending about a month in each area collecting information on homes, available facilities, housing stock, and living conditions.

India's population is now estimated to be more than 1.4 billion, making it the most populous nation in the world. The previous census, conducted in 2011, recorded a population of 1.21 billion, when nearly 2.7 million enumerators surveyed more than 240 million households across the country.

The exercise will blend in-person surveys with a digital option that allows residents to submit information through a multilingual smartphone application that integrates satellite-based mapping. More than 3 million government workers are expected to be deployed over the course of the year to carry out the nationwide count.

A second phase, scheduled from September through April 1, will record more detailed information, including people's social and economic characteristics such as religion and caste. That phase will also attempt a broader accounting of caste beyond historically marginalized groups. Caste is an ancient system of social hierarchy in India that influences social standing and access to resources, education, and economic opportunity. There are hundreds of caste groups based on occupation and economic status across the country, particularly among Hindus.

India has limited or outdated data on the number of people belonging to various caste groups. The last attempt to gather detailed caste information through a census dates to 1931, during British colonial rule. Since India's first post-independence census in 1951, the government counted only Dalits and Adivasis — members of marginalized groups known as Scheduled Castes and Scheduled Tribes who qualify for certain government benefits. Successive governments resisted conducting a full caste count, arguing it could heighten social tensions and trigger unrest.

Population data collected through the census underpins the distribution of government welfare programs and a wide range of public policies. The count could also prompt a redrawing of India's political map, as seats in the lower house of Parliament and state legislatures may be increased to reflect population growth. A 2023 law reserves one-third of legislative seats for women, so any expansion would raise the number of seats set aside for female representatives.