The city of Bay Saint Louis is assigned specific ZIP Code(s) by the United States Postal Service (USPS) to make mail delivery accurate and efficient. A ZIP Code in Bay Saint Louis 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 Bay Saint Louis ZIP Code is important not only for mailing purposes but also for location-based services, navigation, and demographic reference.
| Post Office | Bay Saint Louis |
| County | Hancock |
| State | Mississippi |
| ZIP Code | 39520 |
| Post Office | Bay Saint Louis |
| County | Hancock |
| State | Mississippi |
| ZIP Code | 39521 |