Barangay Casilagan

Barangay Casilagan forms part of Rosario, a municipality in La Union, and is classified as a small barangay.

According to the 2020 Philippine census, Barangay Casilagan had a population of 701. This made it the 32nd largest of 33 barangays in Rosario by population, placing it among the smaller barangays of the municipality. Residents of Barangay Casilagan accounted for approximately 1.16% of the total population of Rosario, which stood at 60,278 in the same census year.

The barangay recorded 667 residents in the 2015 intercensal count and 701 residents in the 2020 Census — a net change of +5.1%, consistent with a growing settlement. Barangay Casilagan is officially classified as rural, a designation applied to barangays with lower population density and predominantly non-built-up land use.

Rosario is a municipality comprising 33 barangays, and serves as the governing unit directly responsible for local services in Barangay Casilagan, including public health, sanitation, peace and order, and civil registration. Within the wider province of La Union, which contains 576 barangays across its component cities and municipalities, Barangay Casilagan ranks 467th by 2020 population. La Union 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 Casilagan 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.