San Sebastian comprises 14 barangays with an estimated population of 11,482. 12 of its barangays (86%) are connectivity dead zones with no recorded cell tower from either the national registry or crowdsourced data.
| Barangay | Population | Towers | Coverage |
|---|---|---|---|
| Balogo | 75 | 0 | Dead zone: no towers from any source |
| Bontod | 564 | 0 | Dead zone: no towers from any source |
| Cabaywa | 448 | 0 | Dead zone: no towers from any source |
| Camanhagay | 1,573 | 0 | Dead zone: no towers from any source |
| Campiyak | 62 | 0 | Dead zone: no towers from any source |
| Canduyucan | 2,122 | 1 | Crowdsourced signal only (no registered tower) |
| Dolores | 1,119 | 0 | Dead zone: no towers from any source |
| Hita-asan I | 608 | 0 | Dead zone: no towers from any source |
| Hita-asan II | 840 | 0 | Dead zone: no towers from any source |
| Inobongan | 1,800 | 2 | Crowdsourced signal only (no registered tower) |
| Poblacion Barangay 1 | 793 | 0 | Dead zone: no towers from any source |
| Poblacion Barangay 2 | 12 | 0 | Dead zone: no towers from any source |
| Poblacion Barangay 3 | 157 | 0 | Dead zone: no towers from any source |
| Poblacion Barangay 4 | 1,309 | 0 | Dead zone: no towers from any source |