San Ildefonso is a municipality in Bulacan province, located in the Central Luzon region of the Philippines. It is situated in the northern part of the province and is part of the greater Metro Manila metropolitan area's northern extension.
The municipality is primarily residential and agricultural in character, with rice farming and other agricultural activities forming the basis of the local economy. Like other municipalities in Bulacan, San Ildefonso has experienced gradual urbanization due to its proximity to Metro Manila.