About the 1940 Census
The first Federal Population Census was taken in 1790, and has been taken every ten years since. However, data from recent censuses are not available because of a 72-year restriction on access to the Census. Most researchers find it helpful to begin with most recent Census that has been released and work backwards to locate people in earlier generations.
Most of the 1890 Census was destroyed in a Department of Commerce fire, though partial records are available for some states.
Census information is available at:
Earlier census records are available at the library through subscription databases (Ancestry and Heritage Quest), microfilm and in books.