It is geographically located on the northern portion of Pangasinan lying within the provincial boundaries of La Union and Benguet. It has a total land area of 137.88 square kilometers. It is bounded on the north by Rosario (La Union), Tuba (Benguet); on the south by Pozorrubio; on the southeast by San Manuel and Binalonan.
The municipality is approximately 200 kilometers north of Manila, 50 kilometers south of San Fernando City, where the regional office of the national goernment agencies in Region I are located, 53 kilometers east of Lingayen (via Pozorrubio), the capital of Pangasinan, and 43 kilometers south of Baguio City.
According to the 2000 census, it has a population of 40,955 people in 8,015 households.
Sison is politically subdivided into 28 barangays.