Long before Diffun was created as municipality in 1950, the place that is now called Barangay Diego Silang was already constituted as a distinct territory. It was declared as an insular reservation of no-Christians on August 3, 1928 by then Governor-General Henry L. Stimpson. The area covered by the reservation was 4,395 hectares, sprawled over the foot of the Namamparang Range at the western side of what is now Quirino Province.
Lush, verdant, and teeming with wild games, the forested reservation soon attracted adventurous Ilongots, Ilocano’s, Ifugaos and Igorots. They were migrants from far place who settle here and practiced rudimentary agriculture. The settlement was originally called Sitio Batara, after a prominent leader among the first settler. Sitio Batara is histocally considered to be the first sitio of Guribang. Eventually, Sitio Batara was renamed Calaocan and became separated from Barangay Guribang.
In time the local population grew prospered. In 1972, during the administration of then Provincial Governor Dionisio Sarandi and Diffun Mayor Mariano Pimentel, Calaocan was politically renamed Diego Silang in honor of a great Filipino hero by that same name.
On August 10, 1994 the people of Diego Silang signed a petition seeking the survey, subdivision, and titling of the parcels of land actually occupied by the residents. The petition was endorsed to the ONCC, and the task of surveying fell upon the hands of the DAR.
With the concerted efforts of the DAR, PARCOM/ PIACIT, ONCC, DENR, and the LGU, then President V Ramos issued Proclamation No. 900 on Oct. 10, 1998 proclaiming the reservation as resettlement project for distribution of DAR in coordination with the DENR, ONCC, and LGU to the actual occupants under CARP.
Barangay Diego Silang is one of the thirty-three barangays of Diffun, Quirino. It is bounded on the north by barangay Guribang, on the east by Barangay San Antonio, on the west by high mountains of the Namamparang Range, and on the south by barangay Maria Clara and Gabriela Silang. Its mains crops are rice, corn, banana, peanuts and vegetables.