Special Cases
How to address an envelope to an inmate
Write the inmate full legal name followed by their inmate, register, or booking number, then the facility name exactly as given, then the facility mailing address, which for many federal and some state facilities is a PO Box rather than a street address. Leave off the number and the letter is very likely to be rejected or delayed, even if every other line is correct, because the number, not the name, is how a facility actually locates a specific person among thousands of residents.
Checked September 28, 2026/8 min read
Written by Claire PostReviewed against USPS Publication 28
What is on this page6 sections
An inmate address looks like it should work the same way as any other envelope, and structurally it almost does: a name, then something in place of a street line, then a facility address. What is different is which line actually gets a letter delivered. On an ordinary envelope, the name carries the address. Here, the identifying number does, because a facility can hold thousands of people and a name alone is not how staff locate one of them.
That single difference is why so much of getting this right is procedural rather than formatting. The name and number have to match the facility’s own records, exactly, the same way a military address has its own fixed structure that does not bend to how a sender happens to think about it. A facility mailroom is not reading the envelope the way a mail carrier reads a residential one; it is matching it against an intake system, and anything that does not match cleanly gets set aside rather than delivered.
The other real difference is the return address. Everywhere else on this site, a return address is optional, a courtesy that only matters if delivery fails. Here it is closer to a requirement: most facilities screen out anonymous mail by policy, independent of whether the rest of the address is perfect.
Step by step
Use the inmate full legal name, not a nickname
Facilities process mail against the name on record at intake, which is a legal name, not whatever the person goes by. A nickname or shortened first name can be enough to get a letter set aside during a manual review.
Put the inmate ID number directly after the name, every time
Called an inmate number, register number (federal), booking number, or DOC number depending on the system, this is how staff physically locate a specific person, especially in a large facility where names alone are not unique. Get it from the inmate directly, from the sending facility, or from the state Department of Corrections or federal Bureau of Prisons online inmate locator.
JOHN SMITHANY COUNTY DETENTION CENTER123 JAIL RDANYTOWN ST 12345CorrectA letter to someone in a county jail, addressed by name and booking number. Copy the facility name and address exactly as given
Do not shorten or guess at a facility name, and do not assume a facility has a normal street address. Many federal and some state facilities receive mail at a specific PO Box tied to that facility, not the building physical location, and a letter sent to the physical address instead can be delayed or returned.
Add a housing unit or pod number if the facility uses one
Larger jails and some state prisons organize residents by housing unit, pod, or dorm, and expect that on the address line below the facility name. A smaller facility or one holding fewer people may not need this at all, so check the specific facility rather than adding it as a default.
JANE DOEFEDERAL CORRECTIONAL INSTITUTIONPO BOX 4000ANYWHERE ST 54321CorrectA letter to someone in the federal system, addressed by name and register number. Always include your own return address
Unlike ordinary mail, most facilities reject or discard anything with no return address on principle, as part of screening for contraband and unidentifiable senders. This is one of the few cases on this site where a return address functions as a requirement rather than an optional courtesy.
Quick reference
| Facility type | Identifier used | Typical address format |
|---|---|---|
| County or city jail | Booking number | Street address, sometimes with a housing unit or pod |
| State prison | DOC or inmate number | Street address or a facility-specific PO Box, plus housing unit |
| Federal (Bureau of Prisons) | Register number | Almost always a facility-specific PO Box, no street address |
Special cases
The rule above covers most people. Here is what changes for the rest.
What if I do not know the inmate ID number?
Most state Departments of Corrections and the federal Bureau of Prisons publish a free online inmate locator that returns the current number and facility from just a name and, sometimes, a date of birth. A county jail roster search or a call to the facility works the same way for a shorter-term stay. Sending a letter with no number at all risks delay far more often than it risks outright loss, but it is worth the few minutes to look up before mailing.
What happens if the person has been transferred to a different facility?
Some systems forward mail to the new facility automatically for a limited window after a transfer; others do not forward at all and simply return the piece. Because this varies by system and is not something a sender can rely on, it is worth checking the inmate locator again before resending rather than assuming the last address you used is still correct.
Are there restrictions on what I can include besides a letter?
Yes, and they vary considerably by facility, often covering things like photo count and size, stickers, tape, perfume, glitter, colored ink, or greeting cards with any electronic or musical component. Because these rules are set and changed by each individual facility rather than by any single national standard, check the specific facility mail policy before including anything beyond a plain paper letter.
Can I address mail using the person street name or alias if that is what I know them by?
No. Facilities process incoming mail against the committed legal name on file, and an alias alone, without the correct legal name and ID number, is one of the more common reasons a piece gets set aside during intake review rather than delivered.
Key terms on this page
- Register number
- The identifying number the federal Bureau of Prisons assigns to a person in its custody, used on the address the same way a name is used on ordinary mail.
- DOC number
- A state Department of Corrections identifying number, the state-level equivalent of a federal register number.
- Booking number
- The identifying number assigned when someone is booked into a county or city jail, typically shorter-term than a state or federal number.
- Mail intake review
- The screening process a facility mailroom runs on incoming mail before it reaches a resident, checking for a correct name and number, a return address, and compliance with that facility content rules.