Pangasinan was among the earliest political and administrative units in the Philippines. It was officially conquered and colonized by D. Martin de Goiti in 1571. On April 5, 1572, Pangasinan was made an encomienda by the Spanish royal crown to receive instructions on the Catholic faith, which means that Pangasinan was organized under one leadership and has identity before the Spanish Royal Court.  Eight years later, in 1580,   Pangasinan  was  organized into a political unit under an alkalde mayor who at that time has authority as head of the province or provincial government with judicial function indicating that Pangasinan has become a province. To commemorate the day when Pangasinan became an encomienda and the year it became a province, Pangasinan celebrates April 5, 1580 as the official founding day of the Province of Pangasinan. At that time, its territorial jurisdiction included the Province of Zambales and parts of La Union and Tarlac. By the middle of the  19th  century  however,  the  northern  towns  of  Agoo to Bacnotan were  separated from the  province and became parts of La Union. The provincial territory was further diminished in 1875 with the annexation of Paniqui and other towns south of it to Tarlac.

Pangasinan,  derived its  name  from  the  word  “panag asinan” , which means “where salt  is made”, owing to the rich  and fine  salt  beds  which  were the prior  source of  livelihood of the province’s coastal towns.