During the early days, a Spanish Mestizo named Don Liberato Bayaua acquired the plains and hills of Diffun as his hacienda by virtue of a Titulo Enformacion de Possessoria. He established a cattle ranch at then the Sitio Buntotan. One of the Guardia Civil at his ranch suffered celebral malaria and died after a few days. A quack doctor termed the cause of death as siphon but two Ilocanos mispronounced it as dipon. Since then, the place was known in its present name as Diffun.

Since 1926, Diffun was claimed as part of Isabela Province, particularly the Municipality of Santiago. But in 1932, further researches conducted by the Municipal Officials showed that Diffun lies within Nueva Vizcaya Province. It took more than two decades of the provinces to settle their jurisdictional claims of the area until it was finally resolved and created as a separate municipality. Hence, Diffun had obtained its identity as a municipality in 1950 by virtue of Executive Order No. 446, series of 1950 thru then President of the Republic of the Philippines, His Excellency, Elpidio Quirino.

Diffun is the gateway to the Province of Quirino. Majority of its people were comprises of farmers and diversity of professionals. Its main products are rice, corn, bananas and other root crops. With regards to education, it has 2 National High Schools and a College University.


The municipality of Diffun is one of the six towns which comprise the Province of Quirino. Situated in the northwestern portion of the Province, it is bounded on the north by the Cordon and Santiago of the Province of Isabela; on the south by the municipality of Kasibu of the Province of Nueva Vizcaya; on the west by the Municipalities of Bagabag, Diadi and Quezon of the Province of Nueva Vizcaya; on the east by the Municipalities of Cabarroguis and Saguday of the Province of Quirino.


Composed of 33 Barangays, four of which are considered urban (Andres Bonifacio, Aurora East, Aurora West and Rizal) while the remaining 29 are rural.


The municipality’s total land area (Based on MPDC records) is 35,280 has. It contains a variety of land uses that have developed in response to population and economic growth.


Based on PSA Survey (2020), Diffun has a total population of 56, 102. It comprises of different ethnic groups like Ilocano, Ifugao, Igorot, Bisaya among others.


Diffun has a total Internal Revenue Allotment (IRA) of 161,314,212 for the year 2018 and a total of 18,296,266.97 of tax revenues and non-tax revenues combined for the year 2018.