It is the southernmost barangay of Metro Manila, located in the southern section of the city bordering the province of Laguna.

The total land area of the barangay is 9.596 km2 (3.705 sq mi), the largest in the city.

There are also three legends or myths that possibly explain the origin of Tunasan's name:[2] Tunasan was called "Tunasancillo" during the Spanish colonial period, and it was a barrio and also a part of the vast hacienda owned by the Augustinian Recollects in the pueblo or town of San Pedro Tunasan in the province of La Laguna.

While barangays are the administrative divisions of the city and are legally part of the addresses of establishments and homes, residents also include their respective subdivisions.

[7] SM Development Corporation donated an 8,348-square-metre (89,860 sq ft) property in Laguerta, Barangay Tunasan for residential use.