Walnut has one ZIP Code, 91789, and that ZIP Code has more than one city in it. The Census Bureau's 2020 files show the City of Walnut covering a little over half of 91789's land. The rest belongs to the City of Industry, Diamond Bar, the unincorporated community of Rowland Heights and a strip of Pomona. A mailing address that ends in "Walnut, CA 91789" can sit in any of them.
For the courthouse, that overlap makes no difference. Every part of 91789 is in Los Angeles County, and the court routes the whole ZIP Code area the same way. For naming the right defendant, serving a local government or reading a lease, it can make a real difference. This page covers both, along with the courthouses, the 2027 service changes and the details that help with a Walnut serve. Walnut requests are run from our Sacramento office, about 375 miles north.
Walnut cases and their courthouses
The court's filing court locator lists two communities under 91789, Walnut and City of Industry. In October 2026, both rows returned the same list:
| Walnut case | Filing courthouse | Straight line from central Walnut |
|---|---|---|
| Small claims | West Covina Courthouse, 1427 West Covina Parkway | 5.4 mi |
| Limited unlawful detainer (eviction) | West Covina Courthouse | 5.4 mi |
| Unlimited civil (over $35,000) | Pomona Courthouse South, 400 Civic Center Plaza | 6.1 mi |
| Family law and restraining orders | Pomona Courthouse South | 6.1 mi |
| Limited civil collection | Norwalk Courthouse, 12720 Norwalk Boulevard | 15.0 mi |
| Probate | Stanley Mosk Courthouse, 111 North Hill Street, Los Angeles | 22.4 mi |
| Limited civil that isn't a collection | Stanley Mosk Courthouse | 22.4 mi |
Walnut sits almost halfway between the East District's two filing courthouses. West Covina is slightly closer and takes the high-volume case types, evictions and small claims. Pomona takes the larger civil suits and family cases.
Who governs a 91789 address?
Here's how the Census Bureau's 2020 ZIP Code to place file divides 91789's land:
| Place | Share of 91789 land | Local government |
|---|---|---|
| City of Walnut | about 55.7% | City of Walnut |
| City of Industry | about 18.5% | City of Industry |
| Diamond Bar | about 11.8% | City of Diamond Bar |
| Rowland Heights (CDP) | about 10.9% | County of Los Angeles |
| Pomona | about 2.5% | City of Pomona |
| Other unincorporated land | under 1% | County of Los Angeles |
The table also works in reverse. Most of Walnut is in 91789, but the city reaches a little way into 91724, the Covina ZIP Code, and into 91792, which is mostly West Covina. The locator's rows for those ZIP Codes, including Charter Oak, Covina, West Covina and Woodside Village, all return the same East District courthouses.
Why this matters on a request:
- Suing a city. A claim about a sidewalk, a permit or a city vehicle goes to whichever government actually controls that spot. For Rowland Heights, that's the County of Los Angeles, not Walnut.
- Naming a business. A company with a "Walnut" mailing address may be registered in Industry or Diamond Bar. Use the name and address on its Secretary of State filing.
- Reading a lease. Landlords often copy the postal city. If the city matters to the case, check the assessor's parcel record before filing.
Evictions and small claims at West Covina
West Covina is Walnut's closest courthouse, about 5.4 miles away. The court's directory puts the small claims clerk and the unlawful detainer clerk together in Room 107, (626) 430-2596, open 8:30 a.m. to 4:30 p.m. on court days. The building opens at 8:00 a.m. Eviction ex parte matters are heard at 11:00 a.m. in Department 2, and the court provides free four-hour parking in its designated areas.
A Walnut tenant who is personally handed an eviction summons has 10 court days to answer, according to the Judicial Council's self-help site. When the papers are left with another adult instead, the deadline is longer, because the mailing step adds time.
For a small claims case, the individual limit is $12,500. The plaintiff can't serve the claim, but anyone else 18 or older who isn't a party can, including a process server. Count back from the hearing date before you send the request. A defendant who lives in Walnut or anywhere else in Los Angeles County needs at least 15 days' notice, and one who has moved out of the county needs 20. If the claim names a business, it's served through the agent shown on its Secretary of State record, and the server signs the proof on form SC-104.
Civil and family cases at Pomona Courthouse South
Pomona Courthouse South, 6.1 miles east of Walnut, takes the city's unlimited civil suits, divorces, custody cases and restraining orders. The directory puts the civil unlimited and family law clerks in Room 101 on the first floor. The family law window opens at 8:00 a.m., half an hour before the civil window. Civil ex parte applications go to the clerk's office at 8:30 a.m. and are heard at 9:00 a.m. in the department.
Under Local Rule 2.3(a)(1)(A), an unlimited personal injury case has to be filed in the district where the incident arose. For a collision or fall inside Walnut, the locator's answer is the East District and Pomona Courthouse South. Many other unlimited civil and family cases may be filed downtown at Stanley Mosk instead, under Local Rule 2.3(a)(1)(B).
Each new civil case needs form LACIV 109, the Statement of Location, and a copy of it is served with the summons and complaint. Include it in the PDFs you upload. Represented parties must e-file civil documents under Local Rule 3.4 unless the court grants an exemption.
Papers to serve in Walnut?
When nobody answers the door in Walnut
Personal delivery is always the first goal. When it doesn't work, substituted service lets the server leave the summons and complaint with a competent adult member of the household, at least 18, or with the person apparently in charge at a place of business, and then mail a copy to the same address. Under CCP § 415.20(b), service done that way is complete on the 10th day after the mailing, so build that time into any deadline.
Gated communities and townhome complexes take planning. If the client knows a gate code, a guard-house procedure or a resident who will let the server in, put it on the request. If the property manager has to approve entry, a name and phone number save an attempt. Without a way in, the server can only try the person at another address, such as a workplace.
Restraining orders for Walnut addresses
A Walnut restraining order is filed at Pomona Courthouse South, under the locator, and the restrained person has to receive the papers personally before the hearing. The server can't be the protected person or any other party to the case. After delivery, the server fills out form DV-200 for a domestic violence order or CH-200 for civil harassment, and the petitioner files it with the court before the hearing date.
What changes for Walnut serves in 2027
AB 747 rewrites parts of the Code of Civil Procedure on January 1, 2027. Three changes affect everyday Walnut cases:
- Attempts before substituted service. Under the new CCP § 415.20(b)(2), 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 after substituted service. The new text allows the follow-up copy to go by first-class mail, Priority Mail with tracking, or certified mail with a return receipt.
- Consumer debt. In a consumer debt collection case, at least one attempt has to be made at the debtor's home when that address is known or can be found with reasonable effort.
Posting an eviction summons stays under CCP § 415.45 and still needs a court order. Our AB 747 guide explains the changes, and the proof of service guide covers what the signed proof has to show.
Serving Mt. San Antonio College or the City of Walnut
Mt. San Antonio College is at 1100 North Grand Avenue, Walnut 91789. Students and employees are served like anyone else: personally, at a place where the server can find them. A schedule and an off-campus address make the job much easier than a building name alone.
When a public agency is the defendant, the summons goes to its governing body. CCP § 416.50 lists the clerk, secretary, president, presiding officer or other head of the governing body as the people to receive it. For the City of Walnut, that's usually the City Clerk at City Hall, 21201 La Puente Road. For the college district, name the district exactly as the complaint does and serve its governing board's officer or clerk.
A claim for money against a city or a college district usually has to be presented to the agency before the suit is filed. Check that the claim was filed and rejected before the summons goes out.
Collections and probate outside the valley
A Walnut collection case of $35,000 or less goes to the Norwalk Courthouse, about 15 miles southwest, one of the court's two countywide collection hubs. Norwalk's Civil Clerk's Office is in Room 101, with a limited collections line at (562) 345-0898.
Probate and the smaller non-collection civil cases go downtown to Stanley Mosk, about 22 miles away. Probate citations still need service at Walnut addresses. Tell us which papers need filing first.
A Walnut Service Request, step by step
- Upload up to 5 PDFs on the Service Request form.
- Give the address as the client's records show it, and flag it if the property is in Industry, Diamond Bar or Rowland Heights.
- Add a schedule, a photo and any gate code for the person being served.
- Choose Rush or Standard, and add a West Covina or Pomona filing if you need one.
Get the updates by email. If the person has left Walnut, skip tracing can look for a newer address, and our page on serving corporations explains how to find a company's agent. We make no guarantees for service.
Cities around Walnut
Diamond Bar is 3.3 miles away and West Covina, home of the eviction and small claims court, 3.4. Industry is 4.9 miles off, and La Puente and Pomona are each 5.6. Every city we serve in the county is on the Los Angeles County page, and filing details are on Los Angeles County court filing.