940 Mailing Address: USPS ZIP Code 940 Guide

30 Sep 2026 · Admin · 1,242 words

The 940 mailing address prefix covers a small but well-known cluster of USPS ZIP codes in Northern California, anchored by the city of Redwood City and stretching along the San Francisco Peninsula. If you have ever typed "940" into a shipping form, looked at a return address from the Bay Area, or wondered which towns share this three-digit prefix, this guide walks through every active ZIP code, the cities it serves, and the practical details that help your mail arrive without delay.

What Is the 940 Mailing Address Prefix?

Every USPS ZIP code begins with a five-digit number. The first three digits identify a Sectional Center Facility (SCF), which is a regional sorting hub. The 940 SCF is based at the San Mateo Processing & Distribution Center and processes mail for much of San Mateo County and the northern Santa Cruz Mountains.

Because the 940 SCF is geographically compact, only a handful of ZIP codes fall under it. Most ZIP codes nationwide start with three-digit prefixes that cover much larger regions, so the small size of the 940 group is unusual and worth knowing about if you mail items there regularly.

Quick Fact of the 940 ZIP Codes

• Region: San Francisco Peninsula, California
• SCF location: San Mateo, CA
• Number of active ZIP codes: 13
• Largest city by population: Redwood City
• Counties served: San Mateo County (primary), small Santa Cruz County overlap

Complete List of 940 ZIP Codes

Here is every USPS ZIP code that starts with 940, along with the primary city or community it serves and the county it belongs to.

Notable Geographic Patterns

The 940 ZIP codes fall into two loose groups. The coastal and bayside cities, including Daly City, Pacifica, Half Moon Bay, and San Bruno, generally use the 94010 through 94044 range. The inland Peninsula cities, including Redwood City, Menlo Park, San Carlos, and Belmont, use the 94060 through 94070 range. A small cluster of Sunnyvale ZIP codes (94085 through 94089) extends the prefix into northern Santa Clara County.

The Largest Cities in the 940 Mailing Address Region

Understanding population centers helps when you are mailing to a business or choosing a sorting facility for bulk shipments.

Redwood City (ZIPs 94061–94065)

Redwood City is the county seat of San Mateo County and uses five distinct ZIP codes, more than any other city in the 940 range. The 94061 ZIP is often used as the default for downtown, while 94062 covers the Emerald Hills area and 94063 and 94065 serve other residential and commercial sections.

Daly City (ZIPs 94014, 94015)

Daly City sits just south of San Francisco and is the most populous city in the 940 prefix. The 94014 ZIP covers the northern portion of the city near the county line, while 94015 covers the southern residential neighborhoods.

South San Francisco (ZIPs 94080, 94083)

Known as the "Industrial City," South San Francisco is a major biotech and logistics hub. 94080 is the standard ZIP, while 94083 is reserved for PO Boxes handled at the main post office.

Sunnyvale (ZIPs 94085–94089)

Sunnyvale is technically in Santa Clara County, but several of its ZIP codes still begin with 940 because of USPS routing boundaries. If you are mailing to a tech company in Sunnyvale, double-check the exact ZIP, as the city also uses 94086 and 94087 for the bulk of residential addresses.

Burlingame and San Mateo Adjacent Cities

Burlingame (94010), San Bruno (94066), San Carlos (94070), and Millbrae (94030) round out the major population centers. Each has a single standard ZIP code plus optional PO Box ranges that share the 940 prefix.

How to Verify a 940 Mailing Address

Even within a tight three-digit prefix, mail can be delayed by a wrong ZIP, a missing apartment number, or a misspelled street name. Use these steps before sending anything important.

1. Confirm the ZIP code on USPS.com. The official USPS ZIP lookup tool accepts a street address, city, and state and returns the correct five-digit ZIP plus the four-digit extension if available.
2. Include the full street address with apartment or suite numbers. Many 940 ZIP codes cover multi-unit buildings where missing unit numbers cause significant delays.
3. Use the standard city name USPS recognizes. USPS prefers "El Granada" over "El Granada, Half Moon Bay" even though locals often group the two.
4. Add the ZIP+4 when possible. Adding the four-digit extension can speed up delivery by an entire day for bulk or marketing mail.
5. Print the address in uppercase or follow USPS guidelines. While lowercase is acceptable, uppercase with no punctuation is the USPS-recommended format for the highest deliverability.

Common Mailing Mistakes to Avoid in the 940 Region

Confusing 940 with 941 or 950

The 941 prefix is reserved for San Francisco itself, while 950 covers the South Bay including San Jose. Transposing a digit can send a letter across the Bay Area and back, costing several days of transit time.

Using a Sunnyvale ZIP Outside the 940 Range

Sunnyvale uses ZIP codes that begin with 94085 through 94089, but portions of the city also use 94085 and 94086 for different neighborhoods. Always verify rather than guess.

Forgetting the PO Box ZIP

Many 940 cities have unique ZIP codes for PO Boxes. For example, South San Francisco's 94083 is exclusively for PO Boxes at the main post office. Sending a street address to 94083 or a PO Box to 94080 can lead to returned mail.

When You Might Use a 940 Mailing Address

People search for the 940 mailing address for several practical reasons:

• Sending business correspondence to tech or biotech companies headquartered along the Peninsula
• Applying for jobs and needing a return address in the San Francisco Bay Area
• Setting up a virtual mailbox or mail forwarding service based in California
• Mailing legal documents to county offices in San Mateo County
• Shipping gifts or personal items to family in Redwood City, Daly City, or surrounding towns
• Researching demographic or geographic data for marketing or academic purposes

Fun Facts About the 940 ZIP Range

• The 940 SCF is one of the smallest in California by land area but ranks among the highest in per-capita mail volume because of dense Peninsula cities.
• Several 940 ZIP codes serve unincorporated communities such as La Honda, Loma Mar, and San Gregorio along Highway 1.
• 94025 (Menlo Park) is home to the headquarters of several well-known venture capital firms and is often used as a proxy address for Silicon Valley investors.
• The Pacific coast ZIPs 94018, 94019, 94037, and 94038 cover some of the most scenic rural coastline in California, yet they all funnel through the same SCF as the urban Peninsula.

Final Thoughts on the 940 Mailing Address

The 940 mailing address prefix may look like just three digits, but it represents a tightly connected stretch of the San Francisco Bay Area, from Daly City in the north to Sunnyvale in the south, and from the Pacific coast inland to the Silicon Valley border. Whether you are mailing a letter, shipping a product, or simply curious about the ZIP codes that fall under this prefix, the list above and the verification tips should help your mail land exactly where it should.

For the most accurate results, always run a final check through the USPS ZIP lookup tool before sending important correspondence. ZIP codes can occasionally be reassigned, and a 30-second check can prevent a multi-day delay.

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