When someone mentions The Census to you, it probably brings to mind the national census in the US (if that's where you happen to live) or in whatever other country you call home. There is pretty familiar online access to old national census records in the US, Britain, and Canada, to name a few.
But there are literally thousands of historical censuses that occurred at a less-than-national level. These should not be overlooked in your search for family history, even if you've already found good information in national census records.
Brooklyn Birdseye tea, anyone?
State and local census records may well identify people who were not included in national headcounts, or can provide additional details about family members, including some deep dark secrets. Local censuses may also identify short-lived individuals who weren't alive for the last federal census, and didn't survive long enough for the next.
At a wonderful site called CensusFinder you can access thousands upon thousands of censuses with millions upon millions of records. Most of what you'll find here is from the big three in online census records -- the US, Canada and the UK -- though there are also links to records in Norway and Sweden. There's also a specialty section devoted to Native American census records.
The many different censuses are organized geographically, usually down to the state and county level (or the equivalent, such as province and shire). Some of these are pretty intriguing, like these from my hometown of Brooklyn (Kings County) NY:
- 1796 Directory of Brooklyn
- 1865 State Census of United States Naval Hospital at Brooklyn
- 1875 State Census of Brooklyn Industrial School
- 1875 State Census of Graham Home for Old Ladies
- 1880 Census of Howard Colored Home for Boys
- 1905 State Census of the Salvation Army Rescue Mission
As you can see, there are records here that you're not likely to find elsewhere.
The records themselves are quite a mixed bag. Some are simple text transcripts of historical records, while others provide actual page images of the original census. They come with varying degrees of explanation and context, as well. Most of the links appear to be free, though a few lead to sites where a fee is charged for full access.
Definitely worth some exploration time.
Also explore the main page of Free Genealogy Tools for more, umm, free genealogical tools.
And don't forget to also check for your family history at Ancestry.com and NewspaperArchive.com. These are subscription databases, but they are among the most powerful research tools available for looking into family roots.