[3][4][5] Daguao was in Spain's gazetteers[6] until Puerto Rico was ceded by Spain in the aftermath of the Spanish–American War under the terms of the Treaty of Paris of 1898 and became an unincorporated territory of the United States.

In 1899, the United States Department of War conducted a census of Puerto Rico finding that the combined population of Daguao and Río Abajo barrios (counted with Fajardo) was 1,099.

This extensive protected natural area is home to ecosystems such as wetlands, estuaries, mangrove forests, coral systems, marine habitats, riverbanks and dry forests.

Los Machos wetland in Daguao makes up the 10% mangroves that remain in Puerto Rico.

Barrios (which are, in contemporary times, roughly comparable to minor civil divisions)[14] in turn are further subdivided into smaller local populated place areas/units called sectores (sectors in English).