Bulak was then a barrio of San Rafael. There were very few inhabitants numbering only about 3,000. The early inhabitants were people from neighboring towns and provinces that preferred to settle in this place because of the good prospect of agriculture.

When the Spaniards came, the name Bulak was changed to Hacienda San Juan de Dios because her 15,500 hectares of grazing and farming grounds were claimed by the friars. The people were told to pay tribute. Proceeds from the rentals were used to finance the operation of the San Juan de Dios Hospital in Manila. The Spanish friars though antagonistic towards the Filipinos, could not help admiring the beauty of the numerous natural scenarios God bestowed on the town. Because of their admiration, they changed the name Hacienda de San Juan de Dios to amore fitting one Hacienda Buenavista, a Spanish word which means beautiful scenery.

As the population grew, a chapel was constructed under the parochial jurisdiction of San Rafael. In 1809, Father Juan dela Rosa was named the first Filipino priest of the town. He held such position up to 1911. He was responsible for changing the Bulak to San Ildefonso in honor of Alfonso XII, then the King of Spain and San Ildefonso, its Patron Saint. By the time it was given this name, a tribunal was created finally making it a town in 1877. Between the periods 1905-1906, San Ildefonso was merged with San Miguel due to its low income and inability to finance its expenditures in operating the local government. \n\nAs year went by, more and more people were induced to live in the town. The growth of population promoted the increase of income. The town became capable of meeting its expenses so it consequently ceased being a barrio of San Miguel and became once again an independent town.