Ilocos Sur has 768 barangays across 34 municipalities. 498 barangays (65%) are connectivity dead zones.
| Municipality | Barangays | Dead zones |
|---|---|---|
| Alilem | 9 | 8 (89%) |
| Banayoyo | 14 | 10 (71%) |
| Bantay | 34 | 9 (26%) |
| Burgos | 26 | 25 (96%) |
| Cabugao | 33 | 18 (55%) |
| Caoayan | 17 | 13 (76%) |
| Cervantes | 13 | 6 (46%) |
| City of Candon | 42 | 22 (52%) |
| City of Vigan (Capital) | 39 | 10 (26%) |
| Galimuyod | 24 | 22 (92%) |
| Gregorio del Pilar (Concepcion) | 7 | 7 (100%) |
| Lidlidda | 11 | 11 (100%) |
| Magsingal | 30 | 17 (57%) |
| Nagbukel | 12 | 11 (92%) |
| Narvacan | 34 | 20 (59%) |
| Quirino (Angkaki) | 9 | 9 (100%) |
| Salcedo (Baugen) | 21 | 20 (95%) |
| San Emilio | 8 | 8 (100%) |
| San Esteban | 10 | 5 (50%) |
| San Ildefonso | 15 | 11 (73%) |
| San Juan (Lapog) | 32 | 22 (69%) |
| San Vicente | 7 | 4 (57%) |
| Santa | 26 | 10 (38%) |
| Santa Catalina | 9 | 5 (56%) |
| Santa Cruz | 49 | 37 (76%) |
| Santa Lucia | 36 | 28 (78%) |
| Santa Maria | 33 | 20 (61%) |
| Santiago | 24 | 10 (42%) |
| Santo Domingo | 36 | 25 (69%) |
| Sigay | 7 | 7 (100%) |
| Sinait | 44 | 32 (73%) |
| Sugpon | 6 | 6 (100%) |
| Suyo | 8 | 3 (38%) |
| Tagudin | 43 | 27 (63%) |