The city of Diamond Bar is assigned specific ZIP Code(s) by the United States Postal Service (USPS) to make mail delivery accurate and efficient. A ZIP Code in Diamond Bar helps identify the correct postal area, ensuring that letters, parcels, and packages reach the right neighborhood or post office without delay. For residents, businesses, and visitors, knowing the correct Diamond Bar ZIP Code is important not only for mailing purposes but also for location-based services, navigation, and demographic reference.
| Post Office | Diamond Bar |
| County | Los Angeles |
| State | California |
| ZIP Code | 91765 |