Santa Lucia is a 3rd class municipality located on the southern coastal area of Ilocos Sur Province. It is bounded on the north
by Candon City, on the east by Salcedo, on the south by Santa Cruz, and on the west by South China Sea.
It has a total land area of 49.7 square kilometers and is politically subdivided into 36 barangays.
The town is situated 337 kilometers north of Manila and 70 kilometers south of Vigan City, the provincial capital.