[3] During the Spanish Colonization of Philippines, a native leader named "Dionisio" had cleared the forest land to create a settlement called "Lakdayan".

In 1877 Spanish arrived and renamed "Lakdayan" to "Dionisio" in the honor of humble fisherman founder of the settlement.

During Spanish times, the head of the local government of Concepcion was titled "Kapitan" (captain) and the subordinate leaders in San Dionisio were titled "Tenientes" (lieutenant) and hereditary Cabeza de Barangay (head of barangay).

The Mount Opaw, with the clear views of ocean and islands, is the tallest range with gentle slope with a single peak with trails in several directions to ascent.

San Dionisio has intermediate tropical climate, relatively dry from December to April and wet for the rest of the year.