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.