664k seems very low. Gonna sober SearX this.
edit: It looks like the 664k number is of people in local jails. (Jail Inmates in 2023, BJS) A small portion in the whole of the incarceration system of the US. The same gov site shows the prison population at 1.254 million in 2023 (Prisons Report Series, 2023, BJS). The site prisonpolicy.org shows 5.5 million people under control of the US justice system in 2025. 2 million of those people are in a correctional facility of some kind. The population of the US from the last census in 2024 is 340 million. This is just quick search on a couple of sources, I no longer want to be sober.