Historical data from the Census can be more difficult to find and use than current data. Census methods have changed, and questions have altered over the years. If you are looking for historical data, here are some sources that might help you.
The Census Schedules or the Enumeration Schedules are the handwritten forms that were filled out by census takers. These forms have been microfilmed and digitized. The National Archives and Records Administration digitized the 1940 census schedules. Private companies like Ancestry have digitized the others.