Dating back to 1847, Irosin was an inland valley devoid of human inhabitants and covered by a vast forest with thriving biodiversity, making it one of the last places in the Philippines to be occupied by settlers.

In the early 1800s, most natives lived along the coastal areas, allowing them greater access to commercial, travel, and communication opportunities.

Deeply influenced by Catholicism brought by Spanish friars, the natives of Hin-ay built a makeshift chapel dedicated to Saint Michael the Archange.

Over the years, the original clearing grew into a bustling community, and the settlers requested that church authorities grant San Miguel a status independent from Bulusan.

On December 12, 1879, through a Royal Decree executed by Governor-General Domingo Moriones y Murillo, San Miguel was made a duly constituted pueblo or town.

During that time, Pedro Fruto (1881-1882), Domingo Gamba (1883-1884), and Juan Gallarda (1885-1886) served as public officials with the title Capitanes del Pueblo.

Iros likely represented the image of floodwaters eroding riverbanks and cutting through lands to form another river route.

[6] Dy later received the "Medalya ng Kagitingan" Award in August for leading his 13 policemen to defend Irosin's municipal hall.

Popular attractions include the Mateo Hot and Cold Spring Resort, St. Michael Archangel Roman Catholic Hilltop Church, and protected areas.

Irosin is also an ideal starting point for mountaineering and ecological treks, providing entry and exit to Bulusan Volcano Natural Park (BVNP), one of the remaining tropical forests and a protected area in the Bicol Region.