San Ildefonso, officially the Municipality of San Ildefonso (; ), is a municipality in the province of Ilocos Sur, Philippines. According to the , it has a population of people.
The town was named after Saint Ildephonsus, a 7th century scholar and theologian.
San Ildefonso, like many other places in the provinces at the beginning of the Spanish Regime, did not have a name. Stories have it that sometime in 1625, the town's inhabitants decided to give it a name, but nothing came out after more than five hours of discussions. So while thinking of a name, they decided to go fishing for a week. And while preparing to go fishing, they saw a box floating not far from shore. Wading to reach the box and carrying it ashore, they opened the box to find a statue of Saint Ildephonsus.
The young women of the place carried the statue to the center of the village, where it was enshrined in a small hut for many years. He became the patron saint of the municipality, and his name was decided to become the name of the fledgling municipality.
San Ildefonso was a former rancheria of Bantay before it became a municipality, but because of its size it was annexed to Santo Domingo as a barrio. In 1921, Assemblyman (and future Philippine president) Elpidio Quirino worked to convert San Ildefonso into a municipality again.
On September 28, 2007, San Ildefonso officials (Governor Deogracias Victor Savellano and Rep. Ronald Singson) commemorated the Basi Revolt. Recently, the Sangguniang Bayan of San Ildefonso approved a resolution declaring September 16 as a non-working holiday and named the old road in Barangay Gongogong as Ambaristo street in honor of Pedro Ambaristo, leader of the Basi Revolt. Mayor Christian Purisima enrolled basi as their entry into the âÂÂOne Town; One Productâ (OTOP) program of Governor Savellano.
San Ildefonso is situated from the provincial capital Vigan, and from the country's capital city of Manila.
San Ildefonso is politically subdivided into 15 barangays. Each barangay consists of puroks and some have sitios.
In the 2024 census, San Ildefonso had a population of 8,213 people. The population density was .
The town is rich in rice, corn, sugarcane, malunggay, katuday & fruit-bearing trees such as star apple, chico, mango, camachile & atis. Its main product is basi, a wine made from fermented sugarcane juice; as well as cane vinegar. They also make nutritious ice cream made up of vegetables in Barangay Bungro, and is being popularized by the town's local government.
San Ildefonso, belonging to the first congressional district of the province of Ilocos Sur, is governed by a mayor designated as its local chief executive and by a municipal council as its legislative body in accordance with the Local Government Code. The mayor, vice mayor, and the councilors are elected directly by the people through an election which is being held every three years.
The Sto. Domingo-San Ildefonso Schools District Office governs all educational institutions within the municipality. They also oversee the operations of all private and public elementary and high schools located in Santo Domingo, Ilocos Sur.