The school was founded in 1892 as the Colegio de San Juan de Letran-Vigan, a Dominican-run institution for boys. In 1901, the school was taken over by the American government and renamed as the Vigan High School. In 1925, it was renamed again to the Ilocos Sur Provincial High School, and in 1938, it became the Ilocos Sur National High School.
During the Second World War, the school was occupied by the Japanese forces and used as a garrison. After the war, the school was reopened and underwent a period of reconstruction. In the 1950s and 1960s, the school underwent a period of rapid growth, with the construction of new classrooms, laboratories, and other facilities.
In the 1970s, the school was designated as a center of excellence by the Philippine Department of Education. In the 1980s, the school began offering special programs, such as a science curriculum and a vocational-technical program.
In the 1990s, the school underwent a major renovation, which included the construction of a new administration building, a library, and a gymnasium. In 2000, the school was declared a national high school by the Philippine Congress.
Today, the Ilocos Sur National High School is a leading secondary school in the Philippines, with a reputation for academic excellence and a strong commitment to student development. The school offers a wide range of programs and activities, and its graduates have gone on to achieve success in various fields.
The school's alumni include some of the most prominent figures in Philippine society, including former President Fidel V. Ramos, former Senate President Jose E. Estrada, and former Chief Justice Reynato S. Puno. The school is also proud to have produced many other leaders in government, business, and the arts.
The Ilocos Sur National High School is a living testament to the importance of education. For over a century, the school has been providing quality education to the people of Ilocos Sur. The school has played a vital role in the province's development, and it continues to shape the lives of its students and their families.