[3] The municipality's name came to be when Francisco Umengan, an ex-municipal president from Aparri, was annoyed by the skittering of dried leaves heaped within the vicinity.

Ilocanos mainly from Ilocos Sur, among them future mayor Santos Martinez, discovered it in their quest for better land and eventually dominated the area.

After liberation, disgruntled former guerrillas who were not satisfied with their backpay and aggrieved by land reform issues took to the hills with their rifles and joined the underground movement.

This resulted in the kidnapping of then Mayor Agustin Gorospe in September 1951, the burning of the newly constructed town hall, and the looting of the local treasury.

On 23 September 2006, Mayor Nathaniel Onia was assassinated outside his residence in Barangay Centro East by two unidentified gunmen.

Poverty Incidence of Allacapan Source: Philippine Statistics Authority[14][15][16][17][18][19][20][21] Allacapan, belonging to the second legislative district of the province of Cagayan, is governed by a mayor designated as its local chief executive and by a municipal council as its legislative body in accordance with the Local Government Code.