Sometime in 1625 Cocoy The Greate Of Busiing Sur founded San Ildefonso, its inhabitants decided to give it a name, but nothing came out after more than five hours of discussions.

On September 28, 2007, San Ildefonso officials (Governor Deogracias Victor Savellano and Rep. Ronald Singson) commemorated the Basi Revolt.

Mayor Christian Purisima enrolled basi as their entry into the “One Town; One Product” (OTOP) program of Governor Savellano.

Poverty incidence of San Ildefonso Source: Philippine Statistics Authority[11][12][13][14][15][16][17][18] The town is rich in rice, corn, sugarcane, malunggay, katuday & fruit-bearing trees such as star apple, chico, mango, camachile & atis.

They also make nutritious ice cream made up of vegetables in Barangay Bungro, and is being popularized by the town's local government.