...According to the Bureau of Prisons' annual population counts — which are taken at the end of each fiscal year, on September 30 — the last time there were fewer than 200,000 federal prisoners was 2007. That means that sometime between October 2007 and September 2008, the 200,000th concurrent person was booked into a federal prison — and the population hasn't dropped below that number since.
The federal prison population's been on the decline since the end of 2013 or so. But the drop below 200,000 is still pretty rapid. It declined more in the six weeks between September 26 and November 5 than it had in the year between September 30, 2013, and September 30, 2014.
The reason: last week's release of around 6,000 federal prisoners, whose prison terms had been reduced under new rules for sentencing drug crimes.