The National Archives and Records Administration is the official keeper of archived federal census records.
The Census Bureau has digitized the historical print volumes and made them available as PDFs.
AU's Library subscribes to the database Ancestry Library Edition which is a good source for information about individuals from historic Census data.
AU also subscribes to Social Explorer which contains data from the first Census in 1790 to the present day.
The Census Bureau has more information on the history of the census.
Aggregate statistical data derived from the census are released as soon as they are available.
By law, individual census records are sealed for 72 years, a number chosen in 1952 as slightly higher than the average female life expectancy. The individual census data most recently released to the public is the 1940 census, released in 2012. The 1950 data will be released in 2022.
It is important to remember that it can be difficult to compare demographic data over time, since the questions asked and methods used have not remained consistent.