Dupax del Sur, officially the Municipality of Dupax del Sur, is a 2nd class municipality in the province of Nueva Vizcaya, Philippines. At the 2020 census, it had a population of 21,224 people.

The name Dupax came from the Isinay word "dopaj" which means "to lie down in complete relaxation and rest", the thing the natives wanted to do, upon repairing their camp and eating their catch, after hunting in the forest and before going homes.

Prior to the establishment of Dupax, the site of what would be its town proper served as a camp for hunters from surrounding tribal settlements.

The area, either a plain or a valley, was located near their hunting grounds, and became their settlement as the town of Dopaj. After the Spanish arrived, the name was spelled as Dupax due to the Spanish orthography of the time.

The town of Dupax was first discovered by Luis Pérez Dasmariñas in 1591. Eighteen years later, the mission was established by the Dominicans, but was later abandoned due to territorial disputes with the Franciscans.

Colonization seemed difficult for decades. In 1717, Fr. Alejandro Cacho came on mission to Dupax and established Christian communities. In June 1726, Spanish Augustinian missionaries arrived in the locality. On April 22, 1731, Dupax was formally founded by Fr. Nicolas Norbantes and Fr. Agustin San Juan, making it the oldest surviving municipality of Nueva Vizcaya.

In the early 18th century, Dupax was inhabited by three tribal groups. The Caraos from Benguet lived with the Isinays, the town's first inhabitants, in the present territory. The other two were the Mala-ats and the Bugcalots.

Mala-ats, original settlers found by the Spanish colonizers in Dupax, are said to be ancestors of the Isinais who now inhabit the locality. They were forced to migrate to the hinterlands as ethnic groups from other provinces, especially the Ilocanos, Igorots, lfugaos, arrived before and after the turn of the century.

The original town of Dupax was the largest municipality of Nueva Vizcaya in terms of land area. The first head of the town, was Mandalito, an Ilongot. Eventually three prominent mem representing the three tribal districts were appointed, namely: Dayag, who headed the Mala-ats; Tiun Pising, who headed the Igorots, and Bartolo, who headed the Ilongots.

As early as 1928, during the term of mayor Inocencio Suson, attempts were made to transfer the seat to Barrio Malasin. However, the plan was eventually materialized with a bill authored by Representative Leonardo B. Perez. By virtue of Republic Act (RA) No. 1181 approved on June 20, 1954, the seat of government was transferred from old poblacion to Barrio Malasin.

Dupax was later divided into three separate municipalities. RA No. 6372, sponsored by Representative Benjamin Perez and Senator Leonardo Perez, was approved on August 16, 1971, dividing Dupax into two new municipalities: Dupax del Norte and Dupax del Sur, which would consist the old poblacion of Dupax, designated as the seat of government, nine barrios and fifteen sitios. The creation of this municipality was ratified in a plebiscite held on November 8, 1971; the division was implemented through Presidential Decree No. 586 promulgated by President Ferdinand Marcos on November 20, 1974.

In 1979, through Batas Pambansa Blg. 27 approved by Marcos, the municipality of Alfonso Castañeda was established upon separation of two barangays, including Lublub which was designated the seat of government, and seven sitios in the municipality, along with parts of Dupax del Norte.

Dupax del Sur is politically subdivided into 19 barangays. Each barangay consists of puroks and some have sitios.

The town hosts the San Vicente Ferrer Church (Dupax del Sur), which is also known as the Dupax Church or Dopaj Church. The heritage structure is an 18th-century Baroque church located at Barangay Dopaj. The parish church, under the advocation of Saint Vincent Ferrer, is under the jurisdiction of the Roman Catholic Diocese of Bayombong. The church complex has been declared a National Cultural Treasure by the National Museum of the Philippines in July 2001. Its construction was finished in 1776, making it older than other heritage structures in the entire country.

An earlier church structure of modest design might have been erected before 1773 and records tell that the structure may have been reused as a schoolhouse after the erection of the present church at around 1773 by Father Manuel Corripio, OP. By this time, the church of Tuguegarao by Father Antonio Lobato, OP was already standing. Like the earlier Tuguegarao church, Father Corripio had the church of Dupax made of bricks and even had two kilns made near the church complex, one for firing bricks and the other for preparing lime. The current façade, which mimics the silhouette of the earlier Tuguegarao Cathedral and is reflected on the churches of Bayombong and Bambang in Nueva Vizcaya, dates back to 1776 while each level of the bell tower bears inscription of the years when which it must have been completed. Its original titular patron is the Nuestra Señora del Socorro but was replaced by San Vicente Ferrer soon after the mission was returned to the Dominicans.

The façade is divided by cornices into horizontal segments of plastered brick. The first level features a semicircular arched main portal embellished with clay insets. The main doorway is flanked on both sides by two blind windows with an embossed image of the Holy Eucharist. The second story features a niche and two windows framed by embossed carvings. The triangular pediment is divided into two horizontal sections with the lower half pierced with a deeply recessed oculus and the upper part featuring a relief of a cross. The entire pediment is capped by undulating cornices and seven finials, with the central finial crowned with a cross.

To the left of the façade is the four-level, unplastered, rectangular bell tower. The base features saint's niches similar to that found on the second level of the façade while the second level features long, narrow windows framed with bracket columns. The tower is capped with a decorative parapet and a small cupola surmounted by a cross. The church plaza is enclosed by a low perimeter wall and a replica of an earlier atrial cross.

Two focal points inside the church are the pillars supporting the choir loft. The two, white-washed pillars are embellished with reliefs of cherubs, shells, florals and arabesques. Similar motifs can also be found on the baptistery. The original main altarpiece and pulpit are still intact but the heads of the images in the altarpiece are believed to be replicas of the ivory ones stolen over the course of the church's history.

The Dupax del Sur church is an officially declared National Cultural Treasure of the Philippines. In 2015, the Dampol Bridge was also declared as a National Cultural Treasure, where both heritage sites were collectively named by the National Commission for Culture and the Arts as the San Vicente Ferrer Church Complex and Dampol Bridge of Dupax Del Sur. The declaration remains as the only National Cultural Treasure declaration in the entire Nueva Vizcaya province.

Due to the outstanding cultural value of the town of Dupax del Sur, many scholars have been pushing for its inclusion in the Tentative List of UNESCO World Heritage Sites of the Philippines.

Population census of Dupax del Sur

Year Pop. ±% p.a. 1903 1,946 —     1918 3,669 +4.32% 1939 6,767 +2.96% 1948 8,904 +3.10% 1960 10,993 +1.77% 1970 18,241 +5.19% 1975 10,161 −11.07% 1980 9,632 −1.06%	Year Pop. ±% p.a. 1990 12,297 +2.47% 1995 13,900 +2.32% 2000 16,371 +3.57% 2007 17,354 +0.81% 2010 18,146 +1.64% 2015 19,111 +0.99% 2020 21,224 +2.08%
Source: Philippine Statistics Authority

Poverty incidence of Dupax del Sur

5 10 15 20 2006 15.00 2009 15.39 2012 17.02 2015 14.44 2018 15.98 2021 10.99 Source: Philippine Statistics Authority

Dupax del Sur, belonging to the lone congressional district of the province of Nueva Vizcaya, 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 councilors are elected directly by the people through an election which is being held every three years.

Members of the Municipal Council
(2019–2022)

Position	Name
Congressman	Luisa L. Cuaresma
Mayor	Ruben S. Basconcillo Jr.
Vice-Mayor	Neil M. Magaway
Councilors	Emilio C. Felix
	Ferdinand D. Donguis
	Johnny A. Baguidudol
	Rodel R. Campo
	Educar P. Daran
	Dario L. Dupos Sr.
	Bernard B. Reyes
	Marson B. As-as

The Schools Division of Nueva Vizcaya governs the town's public education system. The division office is a field office of the DepEd in Cagayan Valley region. The office governs the public and private elementary and public and private high schools throughout the municipality.

• Philippine Standard Geographic Code
• Philippine Census Information
• Local Governance Performance Management System
• RA 6372 - Creating the Municipality of Dupax del Sur
• PD 586 - Amending RA 6372, inserting new sections