', officially the ', is a of the Philippines| in the province of,. According to the, it has a population of people.
History
Founded by Agustin Daguro Agpaoa in 1949, by virtue of Executive Order No. 259 dated September 28, 1949 issued by President Elpidio Quirino. The mayor named the new LGU after his first name but on official records, it was named after the patron of the new towm. There are seven towns in Isabela named after its founders but used prefix "San" to remove the idea of being self-serving. In the old days, the present site of San Agustin, Isabela was a hinterland inhabited by headhunting Ilongots and some scattered bands of Aetas locally known as "Pogot". It was then a part of the municipality of Echague. From this historic town sailed forth a band of intrepid pioneers led by Juan Gumpal, Antonio Pintang, and Vicente Taguiam. They penetrated the wilderness and explored the rich valleys along both sides of the Cagayan River. They put up scattered settlements which were often plagued by malaria, and the marauding Ilongots and Pogots but the brave pioneers stayed put and in the end they were able to befriend Ilongots and Aetas and at the same time they were able to lick malaria. Not long after the scattered settlements grew into sitios and one of them was Lakay-lakay on the western side of the Cagayan River. The place is now "Masaya Centro", the seat of the municipal government of San Agustin. When Jones was organized into an independent municipality in 1921, 30 barrios were separated from the municipality of Echague and one of them was Masaya. Because all the barrios of Jones prospered beyond the inhabitants' expectations and since there were no good roads connecting the barrios at that time, the people of Masaya and adjoining barrios petitioned the President of the Philippines to organize the barrios into a regular town. In 1959, the barrio of Uldogan was renamed Laoag. It is the home of the "Nuang Festival" the annual celebration in honor of the sturdy carabao and in recognition of the highly successful Carabao Upgrading Program of the local government, through the Office of the Municipal Agriculturist and its cooperating agencies and stakeholders. The program was commenced in 1993 by then Mayor Jesus M. Silorio. This was continued under the successive administrations of Mayor Virgilio A. Padilla and Mayor Operaflor A. Manuel. Under the latter's leadership, the Nuang Festival was started. Mayor Cesar Agonoy Mondala, won the 2016 Elections with the support of 1 & 1/2 barangay Captain out of 23 Barangay.
Barangays
San Agustin is politically subdivided into 23barangays.
Demographics
In the, the population of San Agustin, Isabela, was people, with a density of.
