Substituted Service in California: What CCP §415.20 Actually Requires

Substituted service is what California law allows when the summons and complaint are not handed directly to the person being served: the papers are left with someone else at a qualifying location, and then mailed. It is governed by Code of Civil Procedure section 415.20, and the statute is more specific than most people expect — about who can be left with the papers, where, and what has to happen afterward. This post walks through what the current statute actually says. (Section 415.20 was recently amended; the version described here is the one in effect now, and the changes arriving January 1, 2027 are covered at the end.)

Two different paths: entities and individuals

Section 415.20 has two main subdivisions, and they work differently.

Serving businesses and entities: subdivision (a)

For defendants served under sections 416.10 through 416.50 — corporations, defunct corporations, joint stock companies and associations, partnerships and associations, and public entities — subdivision (a) allows substituted service in lieu of personal delivery. The elements:

The copy of the summons and complaint is left during usual office hours in the person's office — or, if no physical address is known, at the person's usual mailing address (but not a United States Postal Service post office box);
with the person who is apparently in charge; and
a copy is thereafter mailed, by first-class mail, postage prepaid, to the person to be served at the place where the copies were left.

Notice what subdivision (a) does not require: it is available "in lieu of" personal delivery, without a showing of prior attempts. For entity defendants, leaving the papers at the office with the person apparently in charge, followed by the mailing, is itself a complete method of service under the statute.

Serving individuals: subdivision (b), and "reasonable diligence"

For defendants served under sections 416.60 through 416.90 — which includes individual defendants — the rule is stricter. Substituted service is available only if the papers cannot with reasonable diligence be personally delivered. In other words, you must genuinely try personal service first. Once reasonable diligence is satisfied, the papers may be left:

at the person's dwelling house, usual place of abode, usual place of business, or usual mailing address (again, not a USPS post office box);
in the presence of a competent member of the household, or a person apparently in charge of the office, place of business, or usual mailing address;
who is at least 18 years of age and is informed of the contents of the papers; and
a copy is thereafter mailed, first-class, postage prepaid, to the person served, at the place where the papers were left.

The current statute does not define "reasonable diligence" with a fixed number of attempts — it is judged on the facts. That changes in 2027, as described below. In practice, process servers document each attempt — date, time, address, and what happened — and that record is what supports the diligence showing. On the Judicial Council's proof of service form for a summons, substituted service on an individual is accompanied by a declaration of diligence describing the actions taken first to attempt personal service.

The mailing step is part of the service

Under both subdivisions, the mailing is not a courtesy copy — it is an element of the method of service itself. The statute's sequence is leave-then-mail: the copy is mailed to the person to be served at the place where the copies were left. A substituted serve without the follow-up mailing is incomplete under the statute's own terms, which is why careful process servers treat the mailing (and the record of it) as part of the job, not an afterthought. Legal Hub Group's process serving platform will not generate a proof of service for a substituted serve without the follow-up mailing on the record, for exactly this reason.

Private mailboxes: subdivision (c)

The statute has a special rule for commercial mail receiving agencies (private mailbox stores). If the only address reasonably known for the person to be served is a private mailbox obtained through a commercial mail receiving agency, service may be effected on the first delivery attempt by leaving the papers with the agency, in the manner described in Business and Professions Code section 17538.5, subdivision (d).

What changes on January 1, 2027

The Legislature rewrote section 415.20 in 2025, in two stages. The version described above remains in effect until January 1, 2027. The version that becomes operative on that date makes three notable changes:

Reasonable diligence gets a defined floor. For substituted service on individuals, a party shows reasonable diligence by attempting personal delivery, in good faith, on at least three occasions, on three different days, at three different times.
The mailing options expand. The follow-up mailing may be made by United States Postal Service first-class mail, Priority Mail with tracking, or Certified Mail with return receipt requested, with postage prepaid.
Consumer debt cases get an added requirement. In an action to collect consumer debt as defined in Civil Code section 1788.2, at least one of the service attempts must be made at the dwelling place or usual place of abode of the person to be served, if it is known or determinable with reasonable effort.

How this plays out in the field

A registered process server attempting to serve a fictional defendant, Marcus Vale, might try his apartment on a weekday evening, again on a weekend morning, and again on a weekday afternoon — documenting each attempt. Finding an adult member of the household on the third visit, the server leaves the papers with that person, explains what they are, and mails a copy to Marcus Vale at that address. The attempt log, the substituted delivery, and the mailing together become the proof of service — which is the subject of our guide to California proof of service forms.

Legal Hub Group's process servers document every attempt with GPS-verified field records, and the proof of service is generated from that record. If a serve on your matter needs to hold up, that documentation is what does the holding.

This is general information, not legal advice.