Barangay San Mateo

Classified as a mid-sized barangay, Barangay San Mateo is one of the administrative divisions of Tumauini in Isabela, Cagayan Valley, Philippines.

According to the 2020 Philippine census, Barangay San Mateo had a population of 2,684. This made it the 6th largest of 46 barangays in Tumauini by population, placing it in the upper half of the municipality. Residents of Barangay San Mateo accounted for approximately 3.79% of the total population of Tumauini, which stood at 70,743 in the same census year.

The barangay recorded 2,539 residents in the 2015 intercensal count and 2,684 residents in the 2020 Census — a net change of +5.7%, consistent with a growing settlement. Barangay San Mateo is officially classified as rural, a designation applied to barangays with lower population density and predominantly non-built-up land use.

Tumauini is a municipality comprising 46 barangays, and serves as the governing unit directly responsible for local services in Barangay San Mateo, 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 San Mateo ranks 135th 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 San Mateo 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.