| Siero | Asturias | 33010–33938 | 15 |
| Sierra de Fuentes | Cáceres | 10181 | 1 |
| Sierra de Luna | Zaragoza | 50612 | 1 |
| Sierra de Yeguas | Málaga | 29328–29329 | 2 |
| Sierra Engarcerán | Castellón | 12164–12182 | 3 |
| Siete Aguas | Valencia | 46392 | 1 |
| Siete Iglesias de Trabancos | Valladolid | 47511 | 1 |
| Sigüenza | Guadalajara | 19250–19268 | 8 |
| Sigüés | Zaragoza | 50682 | 1 |
| Siles | Jaén | 23380 | 1 |
| Silla | Valencia | 46460 | 1 |
| Silleda | Pontevedra | 36540–36589 | 10 |
| Silos, Los | Santa Cruz de Tenerife | 38435–38470 | 3 |
| Sils | Girona | 17410–17420 | 2 |
| Simancas | Valladolid | 47130 | 1 |
| Simat de la Valldigna | Valencia | 46750 | 1 |
| Sinarcas | Valencia | 46320 | 1 |
| Sineu | Illes Balears | 07510 | 1 |
| Siruela | Badajoz | 06650 | 1 |
| Sisamón | Zaragoza | 50227 | 1 |
| Sisante | Cuenca | 16700 | 1 |
| Sitges | Barcelona | 08870–08871 | 2 |
| Siétamo | Huesca | 22120–22121 | 2 |
| Soba | Cantabria | 39728–39813 | 5 |
| Sober | Lugo | 27421–27469 | 10 |
| Sobradiel | Zaragoza | 50629 | 1 |
| Sobradillo | Salamanca | 37246 | 1 |
| Sobrado | A Coruña | 15813–15815 | 3 |
| Sobrescobio | Asturias | 33993 | 1 |
| Socovos | Albacete | 02435–02437 | 2 |
| Socuéllamos | Ciudad Real | 13630 | 1 |
| Sojuela | La Rioja | 26376 | 1 |
| Solana de los Barros | Badajoz | 06209 | 1 |
| Solana de Ávila | Ávila | 05691 | 1 |
| Solana del Pino | Ciudad Real | 13593 | 1 |
| Solana, La | Ciudad Real | 13240 | 1 |
| Solivella | Tarragona | 43412 | 1 |
| Sollana | Valencia | 46430–46439 | 2 |
| Solosancho | Ávila | 05130 | 1 |
| Solsona | Lleida | 25280 | 1 |
| Solórzano | Cantabria | 39738–39791 | 2 |
| Somiedo | Asturias | 33840–33841 | 2 |
| Somosierra | Madrid | 28756 | 1 |
| Somozas, As | A Coruña | 15565–15568 | 4 |
| Son Servera | Illes Balears | 07550–07560 | 3 |
| Sondika | Bizkaia | 48150 | 1 |
| Soneja | Castellón | 12480 | 1 |
| Sonseca | Toledo | 45100 | 1 |
| Sopela | Bizkaia | 48600 | 1 |
| Sopuerta | Bizkaia | 48190–48870 | 4 |
| Sora | Barcelona | 08588 | 1 |
| Soraluze / Placencia de las Armas | Gipuzkoa | 20590 | 1 |
| Sorbas | Almería | 04149–04278 | 4 |
| Soria | Soria | 42001–42190 | 5 |
| Soriguera | Lleida | 25566–25593 | 3 |
| Sorihuela | Salamanca | 37777 | 1 |
| Sorihuela del Guadalimar | Jaén | 23270 | 1 |
| Sort | Lleida | 25560–25568 | 3 |
| Sorvilán | Granada | 18713 | 1 |
| Sorzano | La Rioja | 26191 | 1 |