It is spoken by around 610 speakers,[2] most of whom live in the San Ildefonso Peninsula, across the bay from Casiguran, Aurora.
[3] Since then it has been continually documented by the late SIL linguists Thomas and Janet Headland.
[4] A New Testament translation was published in 1979, titled Bigu a Tipan: I mahusay a baheta para ta panahun tam.
[5] Among the languages spoken by Philippine "Negrito" populations, Casiguran Dumagat Agta has been one of the most extensively studied.
[4][7] Casiguran Agta has been described as having eight vowel sounds, compared to the usual four in most Philippine languages.