Statistics are often tricky to find, and historical statistics most of all. There is a wonderful resource in our print reference collection though you might want to keep in mind if looking for most any sort of historical statistics to do with the United States. That set is the Historical Statistics of the United States..., REF HA202 .H57 2006.
The set covers just about everything, population, economics etc. For example, did you know that per capita consumption of soda pop went from 24.3 gallons in 1970 to 51.2 in 1995? Must be all those big gulp cups at the convenience stores and fast food places!