THE United States not only incarcerates a lot of people, it also has a bewildering array of places to put them. There are, of course, jails and prisons: jails are usually run by local jurisdictions (cities or counties) and house either convicted criminals serving short sentences or people awaiting trial. Prisons, or penitentiaries, are run by states or the federal government, and house convicts serving longer sentences. But there are also juvenile-detention facilities, military prisons, immigration-detention and civil-commitment centres (used for court-ordered treatment of the mentally ill; they can be inpatient or outpatient) as well as jails and prisons in Indian and overseas territories, most of which are administered by different government entities. This keeps data on the overall size of America's incarcerated population, as well as information about their crimes, quite fragmented. Yesterday the Prison Policy Initiative (PPI), a criminal-justice research and advocacy group, released a report and chart that draws on various data sources to present a fuller picture of precisely who is behind bars, and for what reason. It's not happy reading. PPI reckons the United States has roughly 2.4m people locked up, with most of those (1.36m) in state prisons. That is more than the International Centre for Prison Studies estimates, but it's in the same ballpark.

Remember, though, that number is static: it does not capture the churn of people in and out of incarceration during a given year. For the population in local jails, PPI used the information in Table 1 of this report, which shows how many people were locked up in jails on June 30th 2012 (the last weekday in June), and came up with 721,654 in local jails, as well as another 22,870 immigration detainees housed in local jails under contract with Immigration and Customs Enforcement (ICE). Around 60.6% of jail inmates have been convicted; 39.4%, which includes the immigration detainees, have not been convicted, either because they had only recently been arrested or because they are awaiting trial and don't have the money to make bail. Look one page earlier in the report, however, and you'll see that local jails admitted a total of 11.6m people between July 1st 2011 and June 30th 2012. Jails with fewer than 50 prisoners had a weekly turnover rate of 131%. Similarly, around 688,000 people are released from prisons each year. This, says the report, "underscores how naive it is to think of prisons as separate from the rest of society", and how crucial it is to provide services inside that will help people once they get out—because with very few exceptions, inmates will eventually come out, and it is in society's interest to ensure they need not be locked up again.

But it also underscores something we've written about before: America locks up too many people for too many things. The number of federal laws has risen from 3,000 in the early 1980s to over 4,450 by 2008. Many of these have poor intent requirements, meaning people are being locked up not to keep the rest of society safe, but for technical violations of laws they may not have known existed. This overreliance on imprisonment can be seen most starkly, and sadly, by looking at the juvenile population, which is just under 71,000 nationally. Around 11,600 are imprisoned for "technical violations" of their probation or parole terms, rather than because they committed a new crime. In 11 states such juvenile prisoners outnumber those in for crimes against other people. In only one state (Massachusetts) did juveniles imprisoned for crimes committed against people comprise a majority of juvenile prisoners. Around 3,000 are locked up for things that aren't crimes for adults, "such as running away, truancy and incorrigibility." Incarcerated children are less likely to graduate high-school and more likely to spend time in prison as adults. If America is interested in reducing its prison population, locking up fewer juveniles for silly reasons would be a good place to start.