Statistics can be found in many places - books, newspapers, journal articles, reports, web sites, etc. When looking for statistics, and the same is true for other types of information, you've got to ask, "who would care enough to study this phenomenon and publish their findings?"
As an example, if you were doing research on asthma in the United States, you might turn to the American Lung Association, a group that is "working to save lives by improving lung health and preventing lung disease" http://www.lung.org/about-us/.
Another approach is to turn to government agencies with broad interests. Each year the U.S. Census Bureau puts out the Statistical Abstract a compendium of "statistics on the social, political, and economic organization of the United States." There are statistics in over 30 broad areas covering everything from agriculture, elections, health and nutrition, population, etc. The Statistical Abstract is available online or in our Reference Collection on the 3rd floor of HLC (Call #: HA202.U62).
Matt Bejune
Coordinator of Library Reference and Instruction