The city of San Marcos is assigned specific ZIP Code(s) by the United States Postal Service (USPS) to make mail delivery accurate and efficient. A ZIP Code in San Marcos 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 San Marcos ZIP Code is important not only for mailing purposes but also for location-based services, navigation, and demographic reference.
| Post Office | San Marcos |
| County | San Diego |
| State | California |
| ZIP Code | 92078 |
| Post Office | San Marcos |
| County | San Diego |
| State | California |
| ZIP Code | 92069 |
| Post Office | San Marcos |
| County | San Diego |
| State | California |
| ZIP Code | 92079 |
| Post Office | San Marcos |
| County | San Diego |
| State | California |
| ZIP Code | 92096 |