The first national Census in Britain was in 1841, but there are several local enumerations of populations of particular parishes and towns, for example:
- The parish censuses listed in the answers to this question
- The 1795 census of the parish of Horsforth in Yorkshire West Riding mentioned on this Genuki page
In the answers to that earlier question, two books/monographs were mentioned
- Census Listings, 1522-1930: Holdings in the British Isles by Gibson and Medlycott
- Pre-1841 Censuses and Population Listings in the British Isles by Colin R Chapman
Neither of these is available online in complete form, though there is a preview of the latter that provides some interesting methodological information about the 1841 Census and its precursors.
But is there a comprehensive source of these records available online, which researchers outside the UK can use? It is worth noting that even though these earlier censuses did not always name everyone in a household, they can still be useful for genealogical purposes, allowing one to establish, for example:
How many households or households of a particular name there were in a particular location, and therefore how likely there are to be multiple people of the same name in that location at that time. (Is that Mary Thing daughter of John Thing the same Mary Thing that is my ancestor? Or was Thing a common name in Whatsitham?)
Number of people per household can help establish of there are any children in that household that you've missed.