The United States has, for instance, 2.3 million criminals behind bars, more than any other nation, according to data maintained by the International Center for Prison Studies at King's College London.
China, which is four times more populous than the United States, is a distant second, with 1.6 million people in prison. (That number excludes hundreds of thousands of people held in administrative detention, most of them in China's extrajudicial system of re-education through labor, which often singles out political activists who have not committed crimes.)
San Marino, with a population of about 30,000, is at the end of the long list of 218 countries compiled by the center. It has a single prisoner.
The United States comes in first, too, on a more meaningful list from the prison studies center, the one ranked in order of the incarceration rates. It has 751 people in prison or jail for every 100,000 in population. (If you count only adults, one in 100 Americans is locked up.)
The only other major industrialized nation that even comes close is Russia, with 627 prisoners for every 100,000 people. The others have much lower rates. England's rate is 151; Germany's is 88; and Japan's is 63.
The median among all nations is about 125, roughly a sixth of the American rate.
http://www.nytimes.com/2008/04/23/world/americas/23iht-23prison.12253738.html?pagewanted=all