Río Grande is a town and municipality located on the eastern edge of Puerto Rico's Northern Coastal Valley. It is positioned north of Las Piedras, Naguabo, and Ceiba; east of Loíza and Canóvanas; and west of Luquillo. The municipality is administratively divided into eight barrios plus Río Grande Pueblo, and it forms part of the San Juan-Caguas-Guaynabo Metropolitan Statistical Area.
A significant portion of El Yunque National Forest lies within Río Grande's territory, including the peak of El Yunque itself. This makes the municipality notable for encompassing a major portion of Puerto Rico's only tropical rainforest national forest, which is a defining geographical feature of the area.