Ilocos Sur in the context of "Mountain Province"

The Ilocos Region (Ilocano: Rehion/Deppaar ti Ilocos; Pangasinan: Rehiyon na Ilocos; Tagalog: Rehiyon ng Ilocos), designated as Region I, is an administrative region of the Philippines. Located in the northwestern section of Luzon, it is bordered by the Cordillera Administrative Region to the east, the Cagayan Valley to the northeast and southeast, Central Luzon to the south, and the South China Sea to the west. The region comprises four provinces: Ilocos Norte, Ilocos Sur, La Union, and Pangasinan, along with one independent-component city, Dagupan City. The regional center is the city of San Fernando in La Union, which serves as the administrative hub of the region. The largest settlement in terms of population is San Carlos City in Pangasinan.

The 2020 Philippine Statistics Authority census reported that the ethnolinguistic group composition of the region is predominantly made up of Ilocanos (58.3%), followed by Pangasinans (29.7%), Tagalogs (4.1%), and various Cordilleran (Igorot) indigenous groups.

Ilocos Norte (English: Northern Ilocos/North of Ilocoscode: eng promoted to code: en ), officially the Province of Ilocos Norte (Ilocano: Probinsia ti Ilocos Norte; Tagalog: Lalawigan ng Ilocos Norte), is a province of the Philippines located in the Ilocos Region. It is located in the northwest corner of Luzon island, bordering Cagayan and Apayao to the east, and Abra to the southeast, and Ilocos Sur to the southwest. Ilocos Norte faces the South China Sea to the west and the Luzon Strait to the north. Its capital is Laoag, which is the most populous settlement in the province.

Ilocos Norte is noted for its distinctive geography and culture. This includes numerous examples of well-preserved Spanish colonial era architecture, particularly Saint William's Cathedral in Laoag with its sinking bell tower constructed in the Earthquake Baroque style, the St. Augustine Church in Paoay which is one of UNESCO's World Heritage Sites in the Philippines, and the Cape Bojeador Lighthouse. Famous geographical features include the La Paz Sand Dunes, the beaches of Pagudpud, and the eroded calcarenite Kapurpurawan rock formation in Burgos.

La Union (Tagalog pronunciation: [lɐ ʔʊˈɲon]), officially the Province of La Union (Ilocano: Probinsia ti La Unión; Pangasinan: Luyag na La Unión; Kankanaey: Probinsya di La Unión; Ibaloi: Probinsya ni La Unión; Tagalog: Lalawigan ng La Unión; Spanish: Provincia de La Unión), is a coastal province in the Philippines situated in the Ilocos Region on the island of Luzon. The province's capital, the City of San Fernando, is the most populous city in La Union and serves as the regional center of the Ilocos Region.

Bordered by Ilocos Sur to its north, Benguet to its east, and Pangasinan to its south, with the South China Sea to the west, La Union is located 273 kilometers (170 miles) north of Metro Manila and 57 kilometers (35 miles) northwest of Baguio City. The province spans an area of 1,497.70 square kilometers (578.27 square miles). As of the 2020 census, La Union had a population of 822,352, resulting in a density of 550 inhabitants per square kilometer or 1,400 persons per square mile. The province had 538,730 registered voters as of 2022. The province official language is Iloco (Ilocano), as declared by the provincial government of La Union.

Abra, officially the Province of Abra (Ilocano: Probinsia ti Abra; Inlaod Itneg: Probinsiya ta Abra; Maeng Itneg: Probinsiya di Abra; Moyadan Itneg: Probinsiya ti Abra; Filipino: Lalawigan ng Abra), is a province in the Cordillera Administrative Region of the Philippines. Its capital is the municipality of Bangued, the most populous in the province. It is bordered by Ilocos Norte on the northwest, Apayao on the northeast, Kalinga on the mid-east, Mountain Province on the southeast, and Ilocos Sur on the southwest.