Researchers argue that a profound generational shift by millennials and Gen Zers away from criminal behavior is ending mass incarceration and will ultimately reduce the prison population by 50 percent over the next two decades, with or without accompanying policy reforms.

In a Washington Monthly story last week, Keith Humphreys, Shawn D. Bushway, and Jason Robey declared, "Mass incarceration is ending," citing their new research article published in the Annual Review of Criminology.

Humphreys, a professor of psychiatry at Stanford University and former senior policy adviser in the White House Office of National Drug Control Policy; Bushway, a professor of public administration and policy at the University at Albany's Rockefeller College; and Robey, an assistant professor of sociology and criminology at the University of Iowa, argue that the historic drop in crime over the past 30 years, and a related decline in prison admissions, is due in large part to millennials and Gen Zers entering adulthood with "extraordinarily low rates of criminal involvement and arrest." 

As older generations such as baby boomers and Gen Xers have aged out of criminal behavior, which typically peaks between the late teens and mid-twenties, far fewer millennial and Gen Z offenders have arrived to replace them. Humphreys, Bushway, and Robey conclude that this "generational shift—what demographers call cohort nonreplacement—has already reduced the prison population and will likely continue to do so regardless of the current political climate."

"The punitive machinery still exists, but the receiving bays are empty," they wrote.

However, criminal justice advocates say the political climate is also less hostile than conventional wisdom would have one believe. Although the bipartisan consensus on criminal justice reform in Congress collapsed in 2020, and several states reversed legislative reforms, advocacy groups continued to lobby successfully at the state level.

Udi Ofer, a lecturer on public and international affairs at Princeton University and the former deputy national policy director of the ACLU, published an article in Just Security in March arguing that the narrative of a national backlash against criminal justice reform policies post-2020 ignores the fact that legislation has continued to pass "across red, purple, and blue states, often in a bipartisan manner—even amid heightened political polarization and federal retrenchment."

Data collected by Ofer and his students showed that between 2021 and 2025, states passed at least 654 criminal justice reform laws. The number of reform laws passed increased in 2025, the first year of President Donald Trump's second term.

"These figures do not support the claim that reform has come to a halt," Ofer wrote. "Rather, they suggest a transition away from sweeping legislative reform packages toward more incremental, targeted policy change, often enacted with bipartisan support."

In an interview with Reason earlier this year, Ofer said that while the language that lawmakers may use when talking about the criminal justice system may have changed, they still see the same problems.

"We live in a world right now where there has been a fundamental change in how Americans think of the system, and there's widespread recognition that it's broken," Ofer said.

Ofer argued that, while the criminal justice reform movement didn't accomplish all of its goals by the time it peaked in 2020, the narrative of a popular backlash ignores the massive and continuing changes in the American criminal justice system. Ofer noted that by 2020, incarceration rates in the U.S. had fallen by 31 percent from their 2010 peak. 

Similarly, one of the most often cited statistics of criminal justice reform advocates in the 2010s—that the U.S. has the No. 1 highest incarceration rate in the world—is no longer true.

"We're now No. 5," Ofer said. "Now, is that a cause for celebration? No, we're still an anomaly when it comes to wealthy democracies or really any democracy. But we moved from No. 1 to No. 5, and that's not insignificant."

Humphreys, Bushway, and Robey also warn that the significance of what's happening is being ignored because of stale narratives on both sides of the political aisle.

"Loud voices who preach that Americans with darker skin are inherently criminal cannot cope with a massive fall in crime as the nation moves towards minority-majority status," they write. "Meanwhile, those who characterize America's carceral system as an implacably oppressive lever of an inherently racist country cannot explain a nearly two-decade fall in imprisonment. Yet falling crime and imprisonment are real and should command our attention even if it requires radically new narratives and thinking."

Reason's recent cover story on the history of U.S. prisons argued that America must decide soon what the next era of incarceration will look like. If Humphreys, Bushway, and Robey are correct, the time to decide is already here.

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