The Ilocos Region is located in the northwest of Luzon, bordering to the east the regions of the Cordillera Administrative Region and Cagayan Valley and to the south the region of Central Luzon. To the northwest is the South China Sea.
Region I occupies the narrow plain between the Cordillera Central mountain range and the South China Sea. It also occupies the northern portion of the Central Luzon plain, to the north-east of the Zambales Mountains.
Lingayen Gulf is the most notable body of water in the region and it contains a hundred of islands, including the Hundred Islands National Park. To the north of the region is Luzon Strait.
The Agno river runs through Pangasinan and empties into the Lingayen Gulf. The river flow into a broad delta in the vicinity of Lingayen and Dagupan.