The U.S. prison population, already the largest in the world, grew by 1.9 percent in 2004, leaving federal jails at 40 percent over capacity, according to Justice Department figures.
Inmates in federal, state, local and other prisons totaled nearly 2.3 million at the end of last year, the government said. The 1.9 percent increase was lower than the average annual growth rate of 3.2 percent during the last decade.
According to the International Center for Prison Studies at King's College in London, there are more people behind bars in the United States than in any other country.
China had the second-largest prison population with 1.5 million prisoners, according to statistics updated in April and cited by King's College. The total U.S. population is about 296 million, while China's is 1.3 billion.
The Justice Department said the U.S. incarceration rate hit 486 sentenced inmates per 100,000 last year, up 18 percent from 411 a decade ago.
The five states with the highest incarceration rates last year were all in the South, led by Louisiana with 816 sentenced prisoners per 100,000 state residents. The five states with the lowest rates were all in the North, with Maine experiencing 148 sentenced inmates per 100,000 state residents in 2004.
The U.S. prison population continued to grow last year even though reports of violent crime during 2004 were at the lowest level since the government began compiling statistics 32 years ago, according to a government report, Reuters reports.