[DanBC]

Roughly Americans use prison to refer to places where people are held after being sentenced, and jail to refer to where people are held before sentencing. Or sometimes jail refers to short sentences.

http://www.hg.org/article.asp?id=31513

In England we'd tend to use prison or jail for prisons and "on remand" for people awaiting trial or sentencing, and "police cells" for other stuff.

In the US a lot of prisons have high populations of people with mental illness. See, for example, the use of prisoners to care for other prisoners who have dementia.

http://www.nytimes.com/2012/02/26/health/dealing-with-dement...