[5] San Agustín was known during Spanish times as Guintigui-an because of the abundance of a fish called "tigue" in the area.

Negrito and Mangyan tribes from Panay and Mindoro were the first inhabitants, as well as migrants from island of Romblon, and southern Tablas.

The early settlers found it very tiring at times to cross the channel to Romblon town to attend to civil and religious duties.

The new pueblo or town of Cabolutan progressed slowly and grew more populous despite frequent Moro kidnapping raids.

[6] San Agustin is in the north-eastern part of Tablas Island with a total land area of 14,048 hectares (34,710 acres).

San Agustin has the second highest mountain in the province, the volcano-shaped Mount Payaopao at 2,182 feet (665 m) high, overlooking Carmen Bay.

Pursuant to Chapter II, Title II, Book III of Republic Act 7160 or the Local Government Code of 1991,[14] the municipal government is composed of a mayor (alkalde), a vice mayor (bise alkalde) and members (kagawad) of the legislative branch Sangguniang Bayan alongside a secretary to the said legislature, all of which are elected to a three-year term and are eligible to run for three consecutive terms.

Aside from fishing, an alternative source of livelihood are swine and poultry raising, cottage industries such as raffia production (bags, baskets, mats, hats, etc.)