The Census for the United Province of Canada (usually known even then simply as "Canada") only contained data for the present-day provinces of Ontario and Quebec. This was also true in 1861. New Brunswick and Nova Scotia were independent jurisdictions at the time, but had their own censuses in that year. Most repositories combine the censuses together as one source.
Although a pattern of taking a decennial census had already been established, the 1851 census enumeration did not take place until 12 January 1852. This was due to legislative wrangles which were not solved in time to launch the enumeration in 1851. For this reason, the census is referred to as both the Census of 1851 and the Census of 1852.
The Nova Scotia census contains the names of householders and a statistical analysis by age of the rest of the household. The names of other household members were not collected. In the other three provinces, it was a nominal census.
In some localities (some quite large, such as the City of Toronto), the census records have not survived, so the census data now available for 1851-52 is not complete.
An individual's age was to be expressed as "age next birthday". With the enumeration date so early in the year, in most instances the age given will be that attained by the person during 1852. Therefore, in following one person from the "1851-1852 Census" to the "1861 Census" the age difference should be expected to be 9 years.
Each repository contains slightly different information:
. To cite to this index, please use Source:Canada. Canada Census, 1851 (Index)
Note that there are numerous additional sources at WeRelate that reference the 1851 Canada census for a particular locality, including both indexes and census materials.