Barangay Centro 1 (Pob.)

Barangay Centro 1 (Pob.) forms part of San Guillermo, a municipality in Isabela, and is classified as a mid-sized barangay.

According to the 2020 Census of Population and Housing conducted by the Philippine Statistics Authority, Barangay Centro 1 (Pob.) had a population of 2,575. This made it the 1st largest of 26 barangays in San Guillermo by population, placing it among the most populous barangays of the municipality. Residents of Barangay Centro 1 (Pob.) accounted for approximately 12.31% of the total population of San Guillermo, which stood at 20,915 in the same census year.

The barangay recorded 2,518 residents in the 2015 intercensal count and 2,575 residents in the 2020 Census — a net change of +2.3%, consistent with a growing settlement. The Philippine Statistics Authority classifies Barangay Centro 1 (Pob.) as rural, a designation applied to barangays with lower population density and predominantly non-built-up land use.

San Guillermo is a municipality comprising 26 barangays, and serves as the governing unit directly responsible for local services in Barangay Centro 1 (Pob.), 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 Centro 1 (Pob.) ranks 146th 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.

The barangay's legislative and executive affairs are handled by a Punong Barangay and the Sangguniang Barangay, elected nationwide during the Barangay and SK Elections. The next BSKE is scheduled for Monday, November 2, 2026, following the synchronized election schedule set by COMELEC Resolution No. 11191.