San Diego de Alcalá Church, commonly known as Polo Church, is one of the oldest historical landmarks in Valenzuela City, located about 15.5 kilometers north of Manila. It is under the jurisdiction of the Diocese of Malolos. The original church was completed in 1632, following the establishment of Polo as an independent settlement in 1623. Historical records note that local residents were required to render labor during its construction under the Spanish colonial system.

The church is dedicated to Saint Diego de Alcalá, a Spanish Franciscan lay brother who lived from 1400 to 1463. Known for his humility, simplicity, and service to the poor and the sick, he spent much of his religious life in missionary and charitable work. He was canonized in 1588 and became widely venerated in Spanish territories, including the Philippines, where many early churches were placed under his patronage. His association with healing and compassion made him a significant devotional figure in colonial missions.

During the Second World War, the original structure of Polo Church was largely destroyed by bombing during the Japanese occupation. Only the belfry and part of the entrance façade survived. These remnants are now regarded as the oldest surviving architectural features in Valenzuela and have been preserved by the local community as heritage structures.

A new church building was later constructed adjacent to the ruins. The present church complex reflects both historical continuity and practical adaptation, with the preserved tower serving as a visible reminder of the parish’s early origins.