San Guillermo

The town was named after Eugenio Guillermo, former mayor of Angadanan.

On June 17, 1967, the municipality of San Guillermo was created by virtue of Republic Act No. 4906,^[6] sponsored by Melanio Singson, the then-representative of Isabela's lone district. It used to consist of 15 barangays from Angadanan (i.e. Anonang, Colorado, Calaoagan, Dipacamo, Peredo Edcor, Guam, Nakar, Palawan, Progreso, San Francisco Norte, San Mariano Norte, San Mariano Sur, Villa Rose, Villa Sanchez, and Villa Teresita) and four from Echague (i.e. Aringay, Dingading, San Francisco Sur and Sinalugan).

Due to a noticeable increase in the rate of population migration and potential economic growth, additional barangays were created during the term of Mayor Alvaro Filart, such as barangays Burgos, Dietban, Estrella, Rizal, San Rafael and Villa Remedios. Subsequently, barangay Peredo Edcor was split into two barangays, namely: Centro 1 and Centro 2, which is now the poblacion and the municipality's official seat.^[7]

San Guillermo is situated 69.94 kilometres (43.46 mi) from the provincial capital Ilagan, and 399.93 kilometres (248.50 mi) from the country's capital city of Manila.

In the 2024 census, the population of San Guillermo was 21,043 people,^[15] with a density of 65 inhabitants per square kilometre or 170 inhabitants per square mile.

Poverty incidence of San Guillermo

Source: Philippine Statistics Authority^{[16][17][18][19][20][21][22][23][24]}

Socioeconomic metrics indicate that San Guillermo operates formally as a fourth-income-class municipality within the Philippines. According to the Philippine Statistics Authority, the municipality recorded a poverty incidence rate of 22.09 percent in 2021 among its registered population. A measurable portion of the community experiences persistent food insecurity, prompting the direct intervention of national social welfare initiatives. The Department of Social Welfare and Development included San Guillermo in its Walang Gutom program, which distributes food credits to targeted households to mitigate hunger and malnutrition.^[25] Local economic planning aims to address these poverty metrics by promoting domestic investments in poultry production, commercial crop cultivation, and regulated forest management. The municipal government generates revenue from local business taxes, agricultural trade, and national tax allotments to fund administrative and social services aimed at supporting the local workforce. Financial records for the municipality show reliance on these combined revenue streams to sustain public works and poverty alleviation programs across its twenty-six constituent barangays.

The local economy relies heavily on agricultural production and forestry as its primary sources of livelihood. Data from the municipal government indicates that the local agricultural sector focuses on the cultivation of corn, bananas, and pineapples.^[26] These crops are harvested and subsequently distributed to neighboring municipalities and regional market centers. Local farming operations vary, ranging from small subsistence agriculture to larger organized commercial crop production. To improve farm efficiency and output, national government agencies provide structural support and technical training to local agricultural workers. The Department of Agrarian Reform established a Farm Business School in the municipality to train groups such as the Estrella Danggayan Agrarian Reform Beneficiaries Cooperative. This educational program teaches farmers resource allocation, systematic farm planning, and business management techniques to transition their operations into financially viable agro-industrial enterprises.^[27] Livestock and poultry raising also contribute to the local agricultural output, providing secondary income streams for rural households. The integration of modern farming techniques seeks to establish food security and steady revenue for the local agrarian workforce.

The topography of San Guillermo dictates its specific economic activities and structural land use patterns. The local government reports that the municipality covers a total land area of 45,370 hectares characterized largely by a mountainous, hilly, and rugged landscape. This specific slope classification supports the planting of various fruit-bearing trees and facilitates organized ranching activities across the terrain.^[26] The municipal administration identifies the local forested areas as accessible sources of timber, rattan, and bamboo. Commercial timber production and agro-forestry form a core component of the local livelihood, generating revenue for both the municipality and individual laborers. Geographic constraints and inadequate infrastructure routinely affect economic movement within the territory. The presence of underdeveloped roads and bridges complicates the ability of farmers in rural barangays to transport their harvested goods to centralized market centers. Improving these farm-to-market road networks remains a target for local government development in order to facilitate the steady trade of agricultural and forest products. The terrain, while providing natural resources, necessitates continued infrastructure funding to maintain economic stability.

The Schools Division of Isabela governs the town's public education system.^[30] The division office is a field office of the DepEd in Cagayan Valley region.^[31] The San Guillermo Schools District Office oversees all public and private elementary and high schools within the municipality.^[32]