Santiago, officially the Municipality of Santiago, is a 4th class municipality in the province of Ilocos Sur, Philippines. According to the 2020 cens…Santiago, officially the Municipality of Santiago, is a 4th class municipality in the province of Ilocos Sur, Philippines. According to the 2020 census, it has a population of 19,471 people. Santiago Cove is dubbed as the "Boracay of Ilocos Sur" because of its white sand.