Every ten years the Office for National Statistics (ONS) carries out a census to find out more about the people who live in England and Wales, and about the make-up of local neighbourhoods.
The 2011 Census took place on Sunday 27 March 2011, when the ONS sent out questionnaires for around 25 million households to complete.
The 2011 Census (conducted on 27th March 2011) was the first census in England & Wales which allowed respondents to complete their census form online.
The census asks about work, health, national identity, citizenship, ethnic background, education, second homes, language, religion, marital status and so on.
These statistics are then used to build a picture of today's society.
To find out more, please download a copy of the 2011 Census Household Questionnaire for England.
Like all local authorities in England and Wales, Harrow Council relies on census population statistics to get the government funding we need for public services.
How much we get is directly related to how many and what kind of people the census says live in our area.
On average every person is worth around £500 per year in funding to the council from central government.
So even if the census were to end up just a few households short, it could make a very real difference to people's lives.
The census needs to include everyone, everywhere - and that's why everyone has to take part.