The Difference Between Jail, Prison and Immigration Detention

Jails, prisons and immigration detention facilities operate under different legal and administrative structures. The Prison Policy Initiative's national analysis, "Mass Incarceration: The Whole Pie 2026," published in March 2026, draws these systems together while identifying their differences. Understanding who holds a person is the first step toward finding accurate records and resources.

The report stresses that the United States does not have one criminal legal system but "thousands of federal, state, local, and tribal systems." By its count, together they hold nearly 2 million people in 1,566 state prisons, 98 federal prisons, 3,116 local jails, 1,277 juvenile correctional facilities, 220 immigration detention facilities and 77 Indian country jails, plus military prisons, civil commitment centers, state psychiatric hospitals and prisons in U.S. territories. Those figures were assembled from the newest data available in March 2026, with reference dates ranging from 2019 to 2026.

A plain-language glossary of custody systems

• ✱Local jail. Run by a city or county, often through the sheriff. The report notes that a majority of people in jail are awaiting trial, and that only about 120,000 people on any given day have been convicted, generally serving misdemeanor sentences of under a year.
• ✱State prison. Run by a state department of corrections. The Bureau of Justice Statistics (BJS) describes a prison as a long-term facility that typically holds people with sentences of more than one year.
• ✱Federal prison. Run by the Federal Bureau of Prisons (BOP) for people sentenced in federal court. The report used a BOP population of 153,238 as of January 27, 2026, then removed 8,006 people held there for the U.S. Marshals Service to avoid counting them twice.
• ✱Immigration detention. U.S. Immigration and Customs Enforcement (ICE) holds people civilly, which the report describes as "not for any crime, but simply because they are facing deportation." ICE uses federal, private and state-run facilities as well as local jails under contract.
• ✱Youth facilities. Juvenile detention centers and residential placements tied to the juvenile court system. The report counts 34,000 young people in confinement, including some held in adult facilities and in immigration custody.
• ✱Other settings. Indian country jails, military prisons, civil commitment centers and state psychiatric hospitals each have their own rules.

BJS also notes that Alaska, Connecticut, Delaware, Hawaii, Rhode Island and Vermont run integrated systems that combine prisons and jails, so the usual jail-versus-prison split does not apply there.

Which locator to use

Start with the agency that most likely has authority over the person:

• ✱County or city jail: the sheriff's office or the jail's own website, or a phone call to the jail.
• ✱State prison: the state department of corrections' inmate search.
• ✱Federal prison: the Federal Bureau of Prisons Inmate Locator, which covers people in federal custody from 1982 to the present and can be searched by name or by number, such as a BOP register number.
• ✱Immigration detention: ICE's Online Detainee Locator System.
• ✱Youth facilities: the juvenile court clerk or the state's juvenile justice agency.

A BOP result marked "Released" or "Not in BOP Custody" means the person is not currently held by the BOP. The bureau notes the person may still be held by another agency or be on supervision.

When the building and the agency do not match

A person can sit in one type of facility while answering to another agency. The report notes that some people serve state sentences in local jails because the jail is "renting space" to the state prison system, and that 22% of people detained by ICE were in city and county jails, based on ICE data as of January 7, 2026. BJS counted 65,600 people under state or federal prison jurisdiction housed in local jails at yearend 2023. If one search comes up empty, try the locator for the other agency involved.

What this means for families

• ✱Ask the arresting agency or the court which agency is holding the person, and write down any booking, case or ID number you are given.
• ✱Use our find a facility directory to confirm a facility's name and location, then check the official locator.
• ✱For questions about charges, sentences or immigration status, contact a licensed attorney or the local public defender's office. Our local help directory lists service providers by area.