America’s Declining Prison Population

Stanford psychiatry professor Keith Humphreys assesses why “America’s Incarceration Rate Is About to Fall Off a Cliff.”

For more than 40 years, the United States—a nation that putatively cherishes freedom—has had one of the largest prison systems in the world. Mass incarceration has been so persistent and pervasive that reform groups dedicated to reducing the prison population by half have often been derided as made up of fantasists. But the next decade could see this goal met and exceeded: After peaking at just more than 1.6 million Americans in 2009, the prison population was just more than 1.2 million at the end of 2023 (the most recent year for which data are available), and is on track to fall to about 600,000—a decline of roughly 60 percent.

Discerning the coming prison-population cliff requires understanding the relationship between crime and incarceration over generations. A city jail presents a snapshot of what happened last night (for example, the crowd’s football-victory celebration turned ugly). But a prison is a portrait of what happened five, 10, and 20 years ago. Middle-aged people who have been law-abiding their whole life until “something snapped” and they committed a terrible crime are a staple of crime novels and movies, but in real life, virtually everyone who ends up in prison starts their criminal career in their teens or young adulthood. As of 2016—the most recent year for which data are available—the average man in state prison had been arrested nine times, was currently incarcerated for his sixth time, and was serving a 16-year sentence.

So, what happened? Basically, a crime wave that started in the late 1960s led to draconian sentencing laws, which led to mass incarceration. But the wave has long since crested.

The U.S. had an extremely high-crime generation followed by a lower-crime generation, meaning that the older population is not being replaced at an equal rate. The impact of this shift on the prison population began more than a decade ago but has been little noticed because it takes so long for the huge prison population of longer provenance to clear.

But such a transformation is now well under way. One statistic vividly illustrates the change: In 2007, the imprisonment rate for 18- and 19-year-old men was more than five times that of men over the age of 64. But today, men in those normally crime-prone late-adolescent years are imprisoned at half the rate that senior citizens are today.

This is good news all around:

The benefits of a smaller prison population are not limited to those who would otherwise be locked up and the people who love them. Prisons crowd out other policy priorities that many voters would like the government to spend more money on. In all 50 states, the cost to imprison someone for a year significantly exceeds the cost of a year of K–12 education. But even greater than the financial savings would be the prosperity in human terms: Less crime and less incarceration are profound blessings for a society.

[…]

Society is going to experience the benefits of past decades of lower crime throughout its prison system. The imprisonment rate will be lower in five years and lower still in 10. Prisons will still exist then and still be needed, but the rate at which Americans are confined in them could be lower than anything in the preceding half century. This is the fruit of a lower-crime society—good in and of itself, surely, particularly for the low-income and majority-minority communities where most crime occurs. It will also, of course, be a blessing for those who avoid prison, and for the taxpayers who no longer have to pay for it. The decline in the prison population will be something everyone in our polarized society will have reason to celebrate.

Humphreys offers no explanation for why crime spiked in the late 1960s and declined in the early 2000s. The late Kevin Drum would surely point to the gradual removal of lead from our environment. While I’m sure that’s part of the explanation, my guess is that there are multiple factors involved.