San Ildefonso, officially the Municipality of San Ildefonso (, Kapampangan: Balen ning San Ildefonso) is a municipality in the province of Bulacan, Philippines. According to the , it has a population of people.
The early inhabitants called the area Bulak because of the abundant kapok or bulak trees (Ceiba pentandra), which grew on the hill on which the present town was built.
Bulak was initially a barrio of San Rafael, with only about 3,000 inhabitants, who came from nearby towns and provinces who preferred to settle the land because of its good agricultural prospects.
In the Spanish era, the site was renamed Hacienda San Juan de Dios after 15,500 hectares of grazing and farming grounds were claimed by friars. The people made to pay tribute, with the money from the rentals used to finance operation of the San Juan de Dios Hospital in Pasay. The Spanish friars, though antagonistic toward the natives, admired the beauty of the natural scenery, and so renamed the place Hacienda Buenavista (which means beautiful scenery in Spanish).
As the population grew, a visita was constructed in the area under the parish of San Rafael. In 1809, Father Juan de la Rosa became the first Filipino priest of the town, having the position until 1811. He was responsible for changing the name Bulak to San Ildefonso in honor of Alfonso XII, the reigning King of Spain, and the patron saint, Ildefonsus of Toledo. By the time it was given this name, a tribunal was created finally making it a town in 1877. Between 1903 and 1906, San Ildefonso was merged with San Miguel due to its low income and inability to finance its expenditures in operating the local government.
As years went by, more and more people were induced to live in the town. The growth of population promoted an increase of income. The town became capable of meeting its expenses, so it ceased being a barrio of San Miguel and became once again an independent town.
During the Japanese occupation of the Philippines in 1942, the mansion Bahay na Pula of the Ilusorio family was confiscated by the Imperial Japanese Army. It became their barracks and a place where local so-called comfort women were forced into sexual slavery.
With the continuous expansion of Metro Manila, the municipality is the northernmost part of Manila's built-up area.
San Ildefonso is from Malolos and from Manila.
San Ildefonso is politically subdivided into 36 barangays, as shown in the matrix below. Each barangay consists of 7 puroks and some have sitios.
There are 6 urban and 30 rural barangays.
In the 2020 census, the population of San Ildefonso, Bulacan, was 115,713 people, with a density of .
There are two schools district offices which govern all educational institutions within the municipality. They oversee the management and operations of all private and public, from primary to secondary schools. These are San Ildefonso North District Office, and San Ildefonso South District Office.
The town has numerous public schools offering elementary and high school education. Some of the elementary public schools are:
Some of the public high schools are:
Some of the tertiary schools are:
Some of the private schools offering education