Booking Numbers and Inmate IDs, Explained

01What Is a Booking Number?

Somewhere on the jail's website, next to your loved one's name, there is probably a short string of numbers. It may look like nothing — a random receipt code — but it is one of the most important pieces of information you will collect in the coming days. Almost every practical thing you do to support someone in custody begins by typing that number into a form.

A booking number is the jail's internal tracking number for one person's stay in that facility. Almost everything you will do to help — add money, schedule a visit, address an envelope — will ask you for it.

When a person is booked into a jail, staff create a record for that arrest and intake event and attach a reference number to it. That number ties together their photo, charges, housing location, court dates, phone account, and commissary balance inside that facility's computer system. When you call, write, deposit money, or set up a visit, the staff and the vendors they use search by that number far more reliably than by name — because names get misspelled, but a booking number is exact.

What the number actually unlocks

Before we get into the different names and formats, here is the short version of why this matters. You will typically need the booking number or inmate ID to:

• Set up or add money to a phone account so your loved one can call you.
• Make a commissary deposit so they can buy food, hygiene items, and stamps.
• Address a letter or card correctly so mail actually reaches them.
• Schedule a visit, whether in person or by video.
• Send an electronic message through the facility's approved messaging service.
• Confirm they are still at that facility when you call the jail or check the roster.

02Booking Number, Inmate ID, SO Number, PID: What's the Difference?

One of the reasons this topic feels confusing is that there is no single national word for these numbers. Different states, counties, and even individual facilities use different labels for what is often the same idea, and a single person's record may show more than one number at once. Here are the terms you are most likely to run into.

The names you will see

• Booking number (or book number) — usually tied to one specific arrest and intake. Book someone into the same jail twice and they may get two different booking numbers.
• Inmate number or inmate ID — a general term many jails use for the number that identifies a person inside that facility. It may be the same as the booking number, or a separate person-level number.
• SO number — short for Sheriff's Office number (sometimes SID, for State Identification, at the state level). This is often a person-level number that stays the same across multiple bookings at the same agency.
• PID — Personal Identification or Person ID. Like an SO number, this usually follows the person rather than the individual arrest.
• Jail ID, custody number, resident number, or other local labels — the vocabulary varies, but the function is the same: it is how that system finds your person.

Booking-level versus person-level numbers

The distinction worth understanding is between numbers that describe an event and numbers that describe a person. A booking number is usually event-level: it marks this stay, this arrest. An SO number, SID, or PID is usually person-level: it stays attached to the same individual even if they are booked, released, and booked again years later.

Why care about the difference? Because when a form asks for an ID, using the right one saves you frustration. A phone or commissary vendor tied to a single facility often wants the current booking number. A statewide court or records system may key off a person-level SID. If one number does not pull up a match, it is not always a dead end — it may just be the wrong number for that particular system.

03How Is a Booking Number Different From a Court Case Number?

This is one of the most common mix-ups, and getting it straight will save you real time. A booking number and a court case number are created by two different institutions for two different purposes, and they are almost never interchangeable.

The booking number belongs to the jail and tracks the person in custody. The case number belongs to the court and tracks the legal case. You will usually need both — for different things.

Two systems, two numbers

• The booking number comes from the jail or sheriff. Use it for the practical, day-to-day support tasks: phone, commissary, mail, and visits.
• The court case number (sometimes called a docket number or cause number) comes from the court where the charges are filed. Use it to look up hearing dates, charges, filings, and the judge assigned to the case.
• One person can have one booking number but several case numbers if they face more than one matter — and a single case can outlive many jail stays.

Because they serve different systems, the two numbers rarely work in each other's tools. Typing a court case number into a commissary deposit form will usually fail, and typing a booking number into a court records portal will usually turn up nothing. That is expected, not a mistake on your part.

Keeping the legal side organized is its own job, especially as hearings get scheduled, moved, and rescheduled. For families who want the case file and docket in one place, InMato+ includes a real-time case file with docket alerts, so a changed court date does not slip past you while you are focused on the daily work of staying connected. Whether or not you use a tool for it, jot the case number down next to the booking number — you will reach for both.

04What About ICE A-Numbers and Federal BOP Register Numbers?

If your loved one's situation involves federal charges or immigration authorities, you will meet a different family of numbers. County and city jails use booking numbers; the federal and immigration systems use their own identifiers, and knowing which is which helps you search the right database and reach the right office.

The A-Number (immigration)

In the immigration system, a person is identified by an Alien Registration Number, almost always called the A-Number or A#. It is typically a nine-digit number written after the letter A. This is the number immigration authorities, courts, and detention facilities use to track an individual's immigration matters, and it generally stays with the same person over time rather than changing with each booking.

The BOP register number (federal prison)

In the federal criminal system, the Bureau of Prisons assigns a register number to people in its custody. It is commonly written as several digits with a hyphen (for example, in a five-digits-then-three-digits pattern), though you should always confirm the exact format from official paperwork. The federal inmate locator run by the Bureau of Prisons lets you search by this register number or by name.

• A-Number — immigration (ICE and the immigration courts). Person-level; follows the individual.
• BOP register number — the federal Bureau of Prisons, for federal sentences and holds. Used in the federal inmate locator.
• USM number — some people in the federal process are also tracked by the U.S. Marshals Service, which handles custody before and during federal court proceedings.
• County booking number — still relevant even in these cases, because someone with an immigration detainer or a federal hold may physically be housed in a local county jail under contract.

05Where Do You Find the Booking Number?

There are three dependable places to get the number, and it is worth knowing all three, because on any given day one may be faster or more current than the others.

The three reliable sources

1. Check the online jail roster or inmate locator. Most county jails publish a searchable list — sometimes called “Who's in Jail,” an inmate locator, or a custody search. Search by last name, then open your loved one's record; the booking number is usually shown right on the detail page along with the facility, charges, and dates.
2. Look at the booking sheet or release paperwork. If your loved one has any documents from intake or a bond hearing, the number is often printed near the top. A bail bond agent or attorney working the case will also have it.
3. Call the jail's intake or records line. If nothing is online yet, call the non-emergency intake number and ask staff to confirm the person is in custody and to read you their booking number. Have the full legal name and date of birth ready so they can find the record quickly.

Remember the booking delay. Right after an arrest, a person is still being processed, and their record — including the booking number — may not appear online for several hours, sometimes longer overnight or on a busy weekend. An empty search result in the first hours usually means the paperwork has not caught up, not that anything is wrong.

Because every county runs its own separate website, hunting for the right roster in the middle of the night is its own ordeal. The free InMato multi-county search is built for exactly this: you search across participating county systems in one place, and the results surface the booking number along with the facility's official phone and commissary providers — so you are not left guessing which vendor is the real one.

An empty search in the first hours is almost never a disaster. It usually just means booking is not finished and the number has not posted yet.

06Why You Need It for Phone Calls, Commissary, and Deposits

Here is where the booking number stops being an abstraction and starts mattering every single day. The systems that let you talk to your loved one and send them money are almost all keyed to that number.

Phone and video accounts

Jails contract with specific telecom vendors to handle calls and video visits. To fund calls, you generally create an account with that provider and link it to your loved one by entering the facility and their booking or inmate number. Get the number wrong and the money may load, but not to the person you intended — so double-check it against the roster before you confirm any payment.

Commissary and money deposits

Commissary is the in-facility store where your loved one buys food, hygiene items, writing supplies, and stamps. Money you deposit into their account also often covers phone time and medical co-pays. Deposit forms — online, by phone, or at a kiosk — ask for the facility and the booking or inmate number to route the funds to the correct account.

• Confirm the exact booking number and facility from the roster before you send anything.
• Use only the official provider the facility names. Search results and ads can surface look-alike sites that charge extra fees or worse.
• Save your confirmation number and note the date and amount, so you can trace any deposit that seems to go missing.
• Watch for transfers: money sent to the old facility's account may not follow the person automatically.

07How Do You Address Mail With an Inmate ID?

Mail is one of the most meaningful lifelines you can offer, and it is also one of the easiest things to get returned to sender. Jails sort incoming mail by the recipient's number as much as by name, so leaving it off — or getting it wrong — is a common reason letters never arrive.

Building the address

Every facility publishes its own mailing rules and its own required format, so always confirm the current instructions for that specific jail. As a general pattern, an inmate mailing address usually includes:

1. Line one: your loved one's full legal name as it appears on the roster, followed by their booking or inmate number.
2. Line two: the facility's name.
3. Line three: the facility's mailing street address or P.O. box.
4. Line four: the city, state, and ZIP code.

Use the legal name the jail has on file, not a nickname, and place the booking number exactly where the facility asks for it. Many jails now route personal mail through a separate processing address or scan letters to a digital service instead of delivering the physical paper, so the address for mail may not be the same as the jail's street address. Check the facility's mail page before you send the first letter.

• Confirm the current booking number — if the person has been re-booked or transferred, an old number can misroute the letter.
• Follow content rules exactly: many facilities limit stickers, glitter, crayon, laminated items, and the number of pages or photos.
• Put a complete return address on the envelope, or the letter may be rejected.
• When in doubt, keep it simple: plain paper, plain envelope, legal name, correct number.

08Scheduling Visits and Sending Messages

The same number that funds calls and routes mail also stands behind visits and electronic messaging. Once you have it saved, these systems become far less intimidating.

Visitation

Whether a facility offers in-person visits, on-site video, or remote video from your phone, scheduling almost always starts by identifying your loved one through their facility and booking or inmate number. You typically register as a visitor, look up the person by that number, and pick from available time slots. Getting the number right ensures you are booking time with the correct person and at the correct building — important in large counties that run more than one jail.

Electronic messages

Many jails now offer an approved electronic messaging service — a bit like email or texting, sometimes with photo attachments — run through the same vendor as the phones. To send a message you look up your loved one by facility and number, and often buy message credits much as you would buy phone time. As with every other channel, the number is what connects your note to the right inbox.

• Register early: visitor and messaging accounts can require identity verification that takes a day or two to clear.
• Re-check the facility and number before each session, especially if it has been a while, in case of a transfer.
• Keep your login details with your booking-number notes so you are not locked out when visiting hours open.

Every channel — call, letter, deposit, visit, message — runs through the same small set of facts. Get the name, number, and facility right once, and the rest gets much easier.

09Why Do the Numbers Sometimes Change?

You may set everything up perfectly, then discover a week later that the booking number no longer pulls up a match, or that a deposit bounced. This is disorienting, but it usually has a straightforward explanation, and it is rarely a sign that anything has gone wrong.

The usual reasons a number shifts

• A transfer to another facility. A booking number is local to one jail's system. When a person moves to a different county, to state custody, or to a federal facility, they are typically booked in anew and receive a new local number there.
• A new arrest or re-booking. Because booking numbers are event-level, someone released and then booked again — even at the same jail — often receives a fresh booking number for the new stay.
• A move between the person-level and event-level number. A form that worked with the booking number may later need the SO number or SID, or vice versa, depending on which system you are using.

The good news is that person-level identifiers — an SO number, a state SID, an immigration A-Number, or a federal BOP register number — tend to stay constant even as local booking numbers change. If your loved one moves and the old number stops working, searching by name or by a person-level number often finds the new record.

If keeping up with moves feels like too much to track by hand during an already hard time, an optional InMato+ upgrade adds booking and status alerts, along with bail and attorney referrals and a private family community — so a transfer is something you are told about rather than something you stumble onto.

10Keep One Simple Record — and Be Kind to Yourself

For all the systems this number touches, the way to stay on top of it is refreshingly low-tech: keep one short, reliable record and update it whenever something changes. You do not need an app or a spreadsheet — a single note or an index card is enough.

What to keep in one place

• Full legal name exactly as it appears on the roster, plus date of birth.
• Every number the record shows, each labeled the way the website labels it — booking number, SO number, PID, and so on.
• The current facility name and its mailing and physical addresses.
• The official phone, commissary, and messaging providers for that facility, with your account and confirmation numbers.
• The court case number and next known court date, kept alongside — but clearly separate from — the jail's numbers.

With that one card in hand, the daily tasks stop being a scramble. Adding money, addressing a letter, booking a visit — each becomes a matter of copying a number you already trust into a form, rather than hunting for it under stress every single time.

And be gentle with yourself if the numbers blur together at first. This vocabulary is genuinely confusing, invented by institutions for their own convenience, not for the families who have to learn it overnight. Getting a number wrong once does not set anyone back for long; you simply confirm it against the roster and try again.

You are not behind because a form rejected a number. You are learning a system that was never designed to be easy — and you are learning it out of love.

Because names, formats, and rules differ so much from one facility to the next, treat everything here as a starting map rather than the last word. Confirm the exact number, and exactly where it goes, directly with the jail or the official provider. Once you have done that, you hold the key that opens every door to your person — and that is no small thing.