[9] Santo Tomas is a landlocked municipality situated in the northern portion of the province of Isabela.

It is bounded to the west by Quezon, to the south by Delfin Albano, to the southeast by Tumauini, to the north and northeast by Cabagan and the Cagayan River.

As a municipality in the Province of Isabela, government officials in the provincial level are voted by the electorates of the town.

Santo Tomas, belonging to the first legislative district of the province of Isabela, currently represented by Hon.

[25] The Schools Division of Isabela governs the town's public education system.