Basic Information: What Census Data Are Available?

From census.gov (even the cool tree):

"Although censuses are a source of genealogical information, the Census Bureau does not provide these data. The Census Bureau is not able to locate missing persons, or provide recent information on individuals.

By law, personally identifiable information collected for a decennial census is released to the public after 72 years. The National Archives released the 1940 census on April 2, 2012."

Though there are limitations, the site also contains other information on more recent census data. If you want to find out the most common surnames in the past few decennial censuses or what other genealogical-related information your government holds, check it out!