England & Wales Census Dates
The first really useful census (genealogically) in England and Wales was taken in 1841. A census has been taken every ten years since. The census prior to 1841 was basically a head count, so was not particularly useful and there are few retuns surviving. The hundred year rule prevents the census data being made available to the public for 100 years, hence at the moment it is only possible to access census records prior to 1911. Below is a list of the census dates for each census from 1801 to 2011.
This Wikipedia page gives lots of useful information on censuses in England & Wales: Census in the United Kingdom