| City: | Walnut, California |
| County: | Los Angeles County |
| Timezone: | Pacific (GMT -08:00) |
| Local Time: | 9:38:11 AM |
| Population: | No Population Data |
| Area Codes: | 840 / 909 |
| Classification: | PO Box |
| Coordinates: | 34.0203, -117.8647 |
| Quick Link: |
ZIP code 91788 is a PO Box-only ZIP assigned to the Walnut Post Office in Los Angeles County, California. It doesn't cover a geographic area. Instead, it's a point location representing the post office facility on S Lemon Avenue. The surrounding community receives regular street delivery through ZIP code 91789, which encloses this PO Box ZIP.
The post office maintains 734 PO Boxes and serves 419 business delivery points. With 16 business establishments employing 205 people using this ZIP, it functions as a commercial mailing hub for the Walnut area. Residents and businesses who want a dedicated PO Box address use 91788, while their physical locations fall within 91789.
Walnut sits in the San Gabriel Valley, surrounded by Rowland Heights, Pomona, Diamond Bar, and West Covina. The 91788 ZIP handles PO Box services for this suburban community of the Los Angeles metropolitan area. All mail delivery addresses on S Lemon Avenue route through city carrier routes, and UNIT designations indicate the post office building has multiple business suites.
All addresses route to the post office location on S Lemon Avenue.
ZIP Code 91788 supports both business and residential activity. According to the Business Census (2024), there are 16 business establishments, employing about 144 people with an annual payroll of $6,125,000.
| # Residential Mailboxes: | 0Source: USPS |
| # Business Mailboxes: | 0Source: USPS |
| Total Delivery Receptacles: | 8,238Source: USPS |
| Single Family Delivery Units: | 0Source: USPS |
| Multi Family Delivery Units: | 0Source: USPS |
| # of Businesses: | 16Source: CBP |
| 1st Quarter Payroll: | $1,540,000Source: CBP |
| Annual Payroll: | $6,125,000Source: CBP |
| # of Employees: | 144Source: CBP |
ZIP Code 91788 is located in Los Angeles County, California, within the Los Angeles-Long Beach-Anaheim, CA Metropolitan Statistical Area (CBSA 31080) and California's 38th Congressional District. This Metro area has a population of 0 people, about 0.00% of whom live in ZIP Code 91788, and is subdivided into the Los Angeles-Long Beach-Glendale, CA division. It covers 0 sq mi of land and a water area of 0 sq mi.
| CBSA Name: | Los Angeles-Long Beach-Anaheim, CASource: Census |
| CBSA Number: | 31080Source: Census |
| CBSA Type: | MetroSource: Census |
| CBSA Division: | Los Angeles-Long Beach-Glendale, CA (CBSA Div 31084)Source: Census |
| CBSA Population: | 0Source: Census |
| MSA: | Los Angeles-Riverside-Orange County, CASource: Census |
| Land Area: | --Source: Census |
| Water Area: | --Source: Census |
| Congressional District: | 38Source: USPS |
| Congressional Land Area: | 101.46 sq miSource: Census |
| PMSA: | Los Angeles-Long Beach, CA PMSASource: Census |
| Intro Date: | < 2004-10Source: ZIP-Codes.com |
| Place FIPS Code: | 0683332Source: Census |
| Place Name: | Walnut city; CaliforniaSource: Census |
We could not locate which school district 91788 belongs to, but we will update this once new district data is released. There are no public schools nor private schools with a mailing address in this ZIP Code. Listing Nearby schools instead. It also has 6 colleges, universities or post secondary education institutions nearby which would be a short commute to.
Our sources include trusted federal and licensed data from the United States Postal Service, U.S. Census Bureau, U.S. Geological Survey, Centers for Medicare & Medicaid Services, and the National Center for Education Statistics, along with proprietary datasets created by ZIP-Codes.com. Data last updated on February 1, 2026.