Barangay Old Centro I

Situated in San Mateo, Isabela, Barangay Old Centro I is one of 33 barangays that make up the municipality within Cagayan Valley.

According to the 2020 Philippine census, Barangay Old Centro I had a population of 2,061. This made it the 13th largest of 33 barangays in San Mateo by population, placing it in the middle tier of the municipality. Residents of Barangay Old Centro I accounted for approximately 3.09% of the total population of San Mateo, which stood at 66,663 in the same census year.

Between the 2015 and 2020 censuses, the population of Barangay Old Centro I changed from 2,002 to 2,061, a shift of +2.9% over the five-year period. This places the barangay among those with growing populations in San Mateo. Barangay Old Centro I is officially classified as rural, a designation applied to barangays with lower population density and predominantly non-built-up land use.

San Mateo is a municipality comprising 33 barangays, and serves as the governing unit directly responsible for local services in Barangay Old Centro I, 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 Old Centro I ranks 255th 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 Old Centro I 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.