Bellag was formerly the name of Buenlag which means that it is a place being crossed by a river. It is situated at the northern tip of Gerona bounded by Sitio Umangan, Patalan, Paniqui. Lying at its western portion is Sitio Caniogan which, as its name connotes, was thick with coconut trees. This sitio was later organized into a barrio called Don Basilio to honor the memory of Don Basilio Santiago, the partriarch of the Santiago clan who became the President Municipal of Gerona, Tarlac, from 1916 to 1921. He also owns vast tracts of land in the former sitio. It was organized into a barrio in 1966 during the incumbency of Mayor Esteban M. Arrojo who is the only son of Buenlag to have been elected of this prestigious elective position to date. Lying at the south is Apsayan, while at its eastern boundary is Caturay.
The early settlers came from Bellag, Malasiqui, Pangasinan. They found the place verdant and flourishing with trees and tall talahibs teeming with birds and fish. Wanting to settle in a wider area offering greater opportunities for social and economic advancement, the other settlers moved farther north which is now Paniqui.
Buenlag was formerly a ranch crossed by two rivers one in the east which was fed by the Tarlac River crossing Villa Paz, Ayson, Pinasling passing through Apsayan and Buenlag. A creek flowed to the center of the barrio bringing rich sediments and during of the animals from the ranch which made the land fertile.