Between 1811 and 1979, state and federal governments built 711 prisons in the US. Between 1980 and 2004, they built 936.
This map, compiled by MapStory's Jon Marino with data from the Prison Policy Initiative, shows the proliferation of state and federal prisons in recent decades. The white dots show the slow, steady pace of new prisons between 1811 and 1979, while the black dots show an abrupt escalation of new prisons between 1980 and 2004.
After lawmakers took tough-on-crime stances in the 1980s, America's prison population rose dramatically. All those new prisoners, however, needed a place to be imprisoned, so it's no surprise that the number of prisons in America skyrocketed as well.
Building and managing all these prisons and inmates is quite costly for state and federal governments. That's one of the reasons states have relaxed their prison sentences and drug laws in the past few years, and why the federal government appears to be following with its own reforms.
Many advocates argue more reform is needed. The mass incarceration of people for drug crimes, which disproportionately affects minorities, is one of the reasons advocates are pursuing marijuana legalization and even the decriminalization of heroin, cocaine, and all other drugs.
For more on America's prison system, watch Ezra Klein's interview with the real Piper Kerman from Orange is the New Black: