The total number of people incarcerated in the US has fallen again, with just under 2.1 million people in prison or jail as of 2019. That's the lowest count since the peak of 2.3 million in 2008. When adjusted for population the fall is even more substantial, with the incarceration rate per 100,000 adults now at its lowest for 24 years (810 inmates for every 100,000 adults).
How the pandemic affected the justice system is not yet clear (data for 2020 is not yet out), but longer term declines in crime rates and arrest rates have likely contributed to the shrinking prison population.
Coming down, but still high
Although the US incarceration rate has fallen recently, the US remains the prison capital of the world — incarcerating people at a higher rate than any other country on Earth. Data from World Prison Brief, which measures inmates relative to the entire population (not just adults), pegs the US incarceration rate at about 639 per 100,000 people. That's higher than El Salvador (564), Turkmenistan (552), Rwanda (545) and Cuba (510) and about 6x the rate of Canada.