Barangay Sisim Abajo

Situated in Tumauini, Isabela, Barangay Sisim Abajo is one of 46 barangays that make up the municipality within Cagayan Valley.

According to the 2020 Philippine census, Barangay Sisim Abajo had a population of 108. This made it the 46th largest of 46 barangays in Tumauini by population, placing it among the smaller barangays of the municipality. Residents of Barangay Sisim Abajo accounted for approximately 0.15% of the total population of Tumauini, which stood at 70,743 in the same census year.

The barangay recorded 147 residents in the 2015 intercensal count and 108 residents in the 2020 Census — a net change of -26.5%, consistent with a contracting settlement. Barangay Sisim Abajo 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 Sisim Abajo, 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 Sisim Abajo ranks 1052nd 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.