There are over 15,000 facilites that incarcerate offenders across the United States. Jails are usually run by local law enforcement and/or local government agencies, and are designed to hold inmates awaiting trial or serving a short sentence. Prisons are usually run by the state's Department of Corrections for state convicts and the Federal Bureau of Prisons (FBOP) federal offenders.
A jail is a secure facility that houses three main types of inmates: people who have been arrested and are being held pending a plea agreement, trial, or sentencing; people who have been convicted of a misdemeanor criminal offense and are serving a sentence of (typically) less than 1 year; and people who have been sentenced to prison and are about to be transferred to another facility.
Jails are operated by a county or city government. Jails are also known as detention facilities. Lockups are facilities in smaller communities where one to a few arrestees can be held for a short time pending transfer to a nearby jail/detention center.
A prison is a secure facility that houses people who have been convicted of a felony criminal offense and are serving a sentence of 12 months or more. Prisons are operated by a state government or the federal government.
There are many types of prisons and they are distinguished by the level of custody the offenders are confined to. There are minimum custody prisons that house non-violent offenders or offenders with short sentences. As the facility is more enhanced for securing the inmates, the level type changes from low to medium to high or maximum. A maximinum prison is also known as a penitentiary, security at the highest level of security.
The number of sentenced inmates entering prisons each day is far less than the number of people delivered at the door of US county jails. People who are going to prison know it in advance. They may be transferred from a jail, taken to prison from court after a conviction, or report to prison on a date set by the court.
People released from prison may be released to parole supervision or to some other type of community program. Or they may be released with no supervision at all, if they have served their full term in prison.