The diocese was erected on January 12, 1985, and comprises 14 municipalities in the western part of the province of Pangasinan.

The diocese has experienced no jurisdictional changes since then, and is a suffragan of the Archdiocese of Lingayen-Dagupan.

On the Feast of St. Thomas Aquinas, January 28, 2024, Pope Francis appointed Napoleon Balili Sipalay, Jr., of the Order of Preachers, then-vice rector of the University of Santo Tomas Central Seminary, to be the new bishop of Alaminos.

[2] His episcopal ordination by ordaining Archbishop Socrates Villegas with Bishop Jacinto Agcaoili Jose and Auxiliary Bishop Fidelis Bautista Layog as co-consecrators was held on March 18 at Manaoag Church.

His solemn installation and canonical possession as the fourth bishop of the diocese was held on March 19, 2024 at the Alaminos Cathedral.