Barangay Masaya Sur

Barangay Masaya Sur forms part of San Agustin, a municipality in Isabela, and is classified as a mid-sized barangay.

According to the 2020 Philippine census, Barangay Masaya Sur had a population of 2,481. This made it the 1st largest of 23 barangays in San Agustin by population, placing it among the most populous barangays of the municipality. Residents of Barangay Masaya Sur accounted for approximately 11.23% of the total population of San Agustin, which stood at 22,096 in the same census year.

The barangay recorded 2,499 residents in the 2015 intercensal count and 2,481 residents in the 2020 Census — a net change of -0.7%, consistent with a broadly stable settlement. Barangay Masaya Sur is officially classified as rural, a designation applied to barangays with lower population density and predominantly non-built-up land use.

San Agustin is a municipality comprising 23 barangays, and serves as the governing unit directly responsible for local services in Barangay Masaya Sur, including public health, sanitation, peace and order, and civil registration. Within the wider province of Isabela, which contains 1,055 barangays across its component cities and municipalities, Barangay Masaya Sur ranks 162nd by 2020 population. Isabela is classified as a 1st by the Bureau of Local Government Finance, a category that reflects the province's annual regular income.

Like every Philippine barangay, Barangay Masaya Sur is led by an elected Punong Barangay (barangay captain) supported by seven Sangguniang Barangay members (kagawads), an SK Chairperson, a Barangay Secretary, and a Barangay Treasurer. The next Barangay and Sangguniang Kabataan Elections (BSKE) are scheduled for Monday, November 2, 2026, with officials serving four-year terms under Republic Act No. 12232.