Many statistics are gathered by government agencies (for example, the U.S. Department of Energy) or large organizations (for example, The American Cancer Society.)
However, you can also find good statistics within books or journal, magazine or newspaper articles.
When you find statistics, check the source of the data. In other words, does the book, article or website list where the statistics came from? Do they come from a reputable or well-known source? Also take note of the date. How old is the information? If not, attempt to find statistics from a more trustworthy source.
A Google trick for finding statistics: Google site:.gov (or whatever domain you want to search) to locate only government stats.
The Statistical Abstract of the United States, published since 1878, is the authoritative and comprehensive summary of statistics on the social, political, and economic organization of the United States.