San Agustin is a philippine municipality in the province Isabela in Region II Cagayan Valley which belongs to the Luzon group of islands. The municipality San Agustin is seated about 80 km south-south-west of province capital Ilagan and about 229 km north-north-east of Philippine main capital Manila.
Regarding urbanization San Agustin is classified as partly urban. San Agustin occupies an area of 278.40 km². By the end of 2007 San Agustin was the home of 20,681 residents. Thus by average 74.29 people are living on one km².
Administratively the Municipality of San Agustin is subdivided into 23 barangays. One forms the center of the city wheras the other 22 are in the outlying areas. Some of them are even several kilometers away from the center of the Municipality. The most populous are Calaocan, Rang-ay, Quimalabasa Sur, Santos, Sinaoangan Norte, San Antonio, Dappig, Sinaoangan Sur, Nemmatan, Dabubu Pequeño, Quimalabasa Norte, Panang, Virgoneza, Laoag, Salay.
Among the bigger cities and municipalities in the neighborhood of San Agustin there are Ilagan 79 km north-north-east, City Of Isabela (City Of Isabela) 53 km north-north-east, City Of Santiago 29 km north-west, City Of Cauayan 44 km north, Echague 23 km north-west, Alicia 30 km north, Solano (Nueva Vizcaya) 59 km west, Tumauini 85 km north, San Mateo 44 km north-west as well as 68 km north-west of San Agustin the municipality Roxas.