Census day is 21 March 2021. The census is a unique survey that takes place every 10 years in England and Wales. 
Households can expect to receive an information pack in the post about the Census, which will tell you how to take part in the survey. Many people will be able to complete the survey online, but there will also be the option of completing the survey on paper.
You can read more about the Census on the Office for National Statistics website: https://census.gov.uk/about-the-census