Diffun, officially the Municipality of Diffun (Ilocano: Ili ti Diffun; Tagalog: Bayan ng Diffun), is a municipality in the province of Quirino, Philippines. According to the 2020 census, it has a population of 56,102 people.

Commercial establishments proliferated along the provincial road due to its proximity to Santiago City as the main commercial hub of the region.

Diffun is the most populous town in Quirino Province and is 9 kilometres (5.6 mi) from Cabarroguis, 21 kilometres (13 mi) from Santiago City, and 389 kilometres (242 mi) from Manila.

Diffun is situated 10.99 kilometres (6.83 mi) from the provincial capital Cabarroguis, and 360.48 kilometres (223.99 mi) from the country's capital city of Manila.

Diffun is politically subdivided into 33 barangays. Each barangay consists of puroks and some have sitios.

Poverty incidence of Diffun

Diffun is part of the lone congressional district of the province of Quirino. It is governed by a mayor, designated as its local chief executive, and by a municipal council as its legislative body in accordance with the Local Government Code. The mayor, vice mayor, and the municipal councilors are elected directly in polls held every three years.

The Schools Division of Quirino governs the town's public education system. The division office is a field office of the DepEd in Cagayan Valley region. There are two schools district offices which govern the public and private elementary and high schools throughout the municipality. Theser are Diffun I District, and Diffun II District.