The Algarrobo tree is leguminous, with shiny leaves and purple and white flowers.

Its fruit is the carob bean, which consists of seeds covered by an edible substance, contained in a capsule-shaped pod.

In the eighteenth and nineteenth centuries there was in its jurisdiction a stronghold, the Algarrobo Fort, and Spanish battalions were there, one by the sea and another on the west side of Cerro de El Vigia.

In the mid-twentieth century there was an American battalion located by the sea in the vicinity of Peña Cortada.

In 1899, the United States Department of War conducted a census of Puerto Rico finding that the population of Algarrobo barrio was 1,054.