2011 United Kingdom census

A census of the population of the United Kingdom is taken every ten years. The 2011 census was held in all countries of the UK on 27 March 2011. It was the first UK census which could be completed online via the Internet. The Office for National Statistics (ONS) is responsible for the census in England and Wales, the General Register Office for Scotland (GROS) is responsible for the census in Scotland, and the Northern Ireland Statistics and Research Agency (NISRA) is responsible for the census in Northern Ireland.

The Office for National Statistics is the executive office of the UK Statistics Authority, a non-ministerial department formed in 2008 and which reports directly to Parliament. ONS is the UK Government's single largest statistical producer of independent statistics on the UK's economy and society, used to assist the planning and allocation of resources, policy-making and decision-making. ONS designs, manages and runs the census in England and Wales. In its capacity as the national statistics office for the United Kingdom, ONS also compiles and releases census tables for the United Kingdom when the data from England and Wales, Scotland and Northern Ireland are complete.

In the run-up to the census both the main UK political parties expressed concerns about the increasing cost and the value for money of the census, and it was suggested that the 2011 census might be the last decennial census to be taken.

The first results from the 2011 census, age and sex, and occupied households estimates for England and Wales and Northern Ireland, were released on 16 July 2012. The first results for Scotland, and the first UK-wide results, were published on 17 December 2012. More detailed and specialised data were published from 2013.

The Registrar General John Rickman conducted the first census of Great Britain's population, and was responsible for the ten-yearly reports published between 1801 and 1831. During the first 100 years of census-taking the population of England and Wales grew more than threefold, to around 32 million, and that of Scotland, where a separate census has been carried out since 1861, to about 4.5 million.

From 1911 onwards rapid social change, scientific breakthroughs, and major world events affected the structure of the population. A fire that destroyed census records in 1931, and the declaration of war in 1939, made the 1951 census hugely significant in recording 30 years of change over one of the most turbulent periods in British history.

The 1971 census was run by the newly created Office of Population Censuses and Surveys (OPCS), a body formed by the merger of the General Register Office and Government Social Survey. In 1996 the Office for National Statistics (ONS) was formed by merging the Central Statistical Office (CSO), OPCS and the statistics division of the Department of Employment; the first census it ran was in 2001. In 2008 the UK Statistics Authority was established as an independent body.

A population census is a key instrument for assessing the needs of local communities. When related to other data sources such as housing or agricultural censuses, or sample surveys, the data becomes even more useful. Most countries of the world take censuses: the United Nations recommends that countries take a census at least once every ten years. Twenty-one out of 40 countries in Europe are engaged in the 2010–2011 census round The design for the 2011 census reflected changes in society since 2001 and asked questions to help paint a detailed demographic picture of England and Wales, as it stood on census day, 27 March 2011.