State and federal prison populations dropped in 2016, the Bureau of Justice Statistics (BJS) announced Wednesday, making three successive years of decline in the national incarceration rate.

This decline led to the lowest rate of imprisonment (measured as commitment to a prison for more than one year) since 1997, when the rate was 450 prisoners per 100,000 U.S. population. The 2016 rate was 444 per 100,000.

There were an estimated 21,200 fewer prisoners in state and federal prisons in 2016 as compared against 2015, the BJS reported. Decline in the federal prison population, overseen by the Bureau of Prisons, was responsible for approximately 34 percent of the 2016 drop.

Prison admissions also declined between 2016 and 2015, by 2,300 people. The federal system was responsible for the overwhelming share—2,200 fewer admissions—of that decline.

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