Buenchico beat me to posting the link. It says:
"The 1921 Census of England and Wales has been made available online through an extensive digitisation project with family history website, Findmypast. It is available for you to access in two ways:
1. You can view it online via Findmypast. Access to each record comes with a small fee – you can find details of pricing here: www.findmypast.co.uk/1921-census.
2. Or, for free access, you can visit The National Archives in Southwest London or at our two partner locations: Manchester Central Library on St Peter’s Square in Manchester, and the National Library of Wales in Aberystwyth. At these locations you will be able to view the Census records via the Findmypast website, but without the charges.