Marc Mauer and the good people at The Sentencing Project just came out with their latest report on decarceration. Since the late 1960s this country has seen the number of people incarcerated increase from about 200,000 to 2.4 million, placing the US. on top of the world in both pure numbers of people it locks away and in the rate (per 100,000). Most of this increase had to do with tougher drug penalties, as well as tougher penalties for things like parole violation. It's also due to a greater number of people being sent to prison for offenses that would not have landed them in prison before, as well as a greater number of people staying behind bars for longer periods of time. See the chart below,
Katherine Beckett in her book "Making Crime Pay" charts this trends and discusses the political motivations behind it all as she records a shifting role of the state (going from one of social welfare created in the wake of the Great Depression to one of Social Control, created in the wake of the Civil Rights Movement). Those most effected by this shift in incarceration are poor, non-whites.
Lots of criminologists have been talking about the need to reduce this trend and we expect it to start soon as the money to continue simply is not there (ignoring, of course, the moral reasons).
Well, to make a long story short (too late), here's a report what a number of states are doing to reduce the number of people they house in their prisons.