C/O slots between the recipient's name and the street address. It never replaces either one.
The exact line order, from USPS's own manual
The Domestic Mail Manual writes out the "care of" format for a household sharing someone else's mail receptacle, and the line order it gives is the same order used any time mail is routed through another person, read 2026-09-01:
C/O ROBERT SMITH
123 APPLE WAY
ANYTOWN ST 12345
John Doe is the person the letter is actually for. Robert Smith is whoever's mailbox it is landing in — a host, a relative, an employer. The recipient's name always leads; the c/o name and everything after it describes how to physically reach that mailbox, not who the mail belongs to.
Staying somewhere that isn't yours
Mail forwarded to a friend's or relative's house while you're between addresses is the plainest case: your name on top, "C/O" and their name underneath, their street address after that.
Mail through an employer or representative
An attorney's office, an accountant or an employer that receives mail on someone's behalf takes the same shape — the individual's name first, then c/o the firm, then the firm's address.
Hotels and care facilities
A guest, resident or patient without their own mailbox gets mail the same way: their name, c/o the building or front desk, then the building's own address.
Not the same line as Attention
In care of (c/o)
C/O TOM PEREZ
500 ELM ST
DALLAS TX 75201
Attention (attn)
ACME SUPPLY CO
500 ELM ST
DALLAS TX 75201
A c/o line sits below the recipient's name and routes a piece of mail to a person through someone else's household or address. An Attention line does the opposite job: it sits above the company name and routes mail arriving at a business to one department or person inside it. Our USPS address format guide covers the Attention line in full; neither line does the other's job, and they never appear stacked on top of each other.
Common questions
Where does the c/o line go in the address block?
Directly under the recipient's name and above the street address. USPS's own Domestic Mail Manual writes the order as NAME, then C/O plus the second name, then the street line: JOHN DOE / C/O ROBERT SMITH / 123 APPLE WAY.
Whose name goes first, the recipient's or the c/o person's?
The recipient, the person the mail is actually for, goes on the first line. The c/o name, the person or household it is being routed through, sits on the second line.
Is c/o the same as an Attention line?
No. An Attention line routes mail to a specific person inside a company and sits above the company name. SMKlog sells parcel labels only.
When does a letter actually need a c/o line?
Whenever the person the letter is for does not have their own mailbox at that address: staying with a friend or relative, receiving mail through an employer or attorney, or checking into a hotel or care facility that holds mail for guests.
Does c/o cost anything extra to mail?
No. It is a formatting choice, not a mail class or an add-on service, so it does not change postage on its own.
Where this rule comes from
- USPS, Domestic Mail Manual, Section 508 — the worked "care of" address example and its line order. Read 2026-09-01.
- USPS Publication 28, Section 211 — the recipient / delivery address / last line block the c/o line is added into. Read 2026-09-01.
The manual's example comes from a specific case, a household sharing a rural mail receptacle, but the line order it shows is the one used for c/o addressing generally.