The following are the zip codes in the municipalities and cities of Ilocos Sur.
| Region | Provinces | City/Municipality | Zip Code |
| Region 1 (Ilocos Region) | Ilocos Sur | Vigan | 2700 |
| Region 1 (Ilocos Region) | Ilocos Sur | Tagudin | 2714 |
| Region 1 (Ilocos Region) | Ilocos Sur | Suyo | 2715 |
| Region 1 (Ilocos Region) | Ilocos Sur | Sugpon | 2717 |
| Region 1 (Ilocos Region) | Ilocos Sur | Sinait | 2733 |
| Region 1 (Ilocos Region) | Ilocos Sur | Sigay | 2719 |
| Region 1 (Ilocos Region) | Ilocos Sur | Santo Domingo | 2729 |
| Region 1 (Ilocos Region) | Ilocos Sur | Santiago | 2707 |
| Region 1 (Ilocos Region) | Ilocos Sur | Santa Maria | 2705 |
| Region 1 (Ilocos Region) | Ilocos Sur | Santa Lucia | 2712 |
| Region 1 (Ilocos Region) | Ilocos Sur | Santa Cruz | 2713 |
| Region 1 (Ilocos Region) | Ilocos Sur | Santa Catalina | 2701 |
| Region 1 (Ilocos Region) | Ilocos Sur | Santa | 2703 |
| Region 1 (Ilocos Region) | Ilocos Sur | San Vicente | 2726 |
| Region 1 (Ilocos Region) | Ilocos Sur | San Juan (Lapog) | 2731 |
| Region 1 (Ilocos Region) | Ilocos Sur | San Ildefonso | 2728 |
| Region 1 (Ilocos Region) | Ilocos Sur | San Esteban | 2706 |
| Region 1 (Ilocos Region) | Ilocos Sur | San Emilio | 2722 |
| Region 1 (Ilocos Region) | Ilocos Sur | Salcedo (Baugen) | 2711 |
| Region 1 (Ilocos Region) | Ilocos Sur | Quirino (Angkaki) | 2721 |
| Region 1 (Ilocos Region) | Ilocos Sur | Narvacan | 2704 |
| Region 1 (Ilocos Region) | Ilocos Sur | Nagbukel | 2725 |
| Region 1 (Ilocos Region) | Ilocos Sur | Magsingal | 2730 |
| Region 1 (Ilocos Region) | Ilocos Sur | Lidlidda | 2723 |
| Region 1 (Ilocos Region) | Ilocos Sur | Gregorio del Pilar (Concepcion) | 2720 |
| Region 1 (Ilocos Region) | Ilocos Sur | Galimuyod | 2709 |
| Region 1 (Ilocos Region) | Ilocos Sur | Cervantes | 2718 |
| Region 1 (Ilocos Region) | Ilocos Sur | Caoayan | 2702 |
| Region 1 (Ilocos Region) | Ilocos Sur | Candon | 2710 |
| Region 1 (Ilocos Region) | Ilocos Sur | Cabugao | 2732 |
| Region 1 (Ilocos Region) | Ilocos Sur | Burgos | 2724 |
| Region 1 (Ilocos Region) | Ilocos Sur | Bantay | 2727 |
| Region 1 (Ilocos Region) | Ilocos Sur | Banayoyo | 2708 |
| Region 1 (Ilocos Region) | Ilocos Sur | Alilem | 2716 |
