Statistics can be extremely effective in your public speaking. Choose them well and don't burden your audience with too many.
If you Google for statistics, very often you will come across personal websites that present statistical data. You will be much more persuasive if you can cite a reliable source for the data.
Government agencies are a key source of statistics about the US. If you want information about prisons, try the US Department of Justice, or a state agency such as the California Department of Corrections & Rehabilitation. In some cases, non-profit agencies and international organizations are excellent sources, but beware of political organizations trying to prove a point with statistics.