From the Document: "Local jails in the United States experienced a large decline (down 185,400 inmates) in their inmate populations from June 30, 2019 to June 30, 2020, which can be attributed mainly to the COVID-19 pandemic. The inmate population confined in local jails was 549,100 at the end of June 2020, down from 734,500 at the end of June 2019. The midyear 2020 inmate population was the lowest since 1996, when 518,500 inmates were confined in local jails (not shown in tables). The impact of COVID-19 on local jails began in March 2020, with a drop of 18% in the inmate population between the end of February and the end of March, followed by an 11% drop by the end of April. By the last weekday in April 2020, the number of jail inmates dropped to a low of 519,500. By the end of May 2020, the population increased about 3% and was up another 2% by the end of June 2020. The decline in the inmate population since midyear 2019 resulted from both a reduction in admissions to jails and expedited releases in response to the COVID-19 pandemic from March to June 2020."
NCJ Document Number 255888; National Criminal Justice Document Number 255888
Bureau of Justice Statistics: https://www.bjs.gov/