Santo Tomas, officially the Municipality of Santo Tomas (Ilocano: Ili ti Santo Tomas; Pangasinan: Baley na Santo Tomas; Filipino: Bayan ng Santo Tomas), is a municipality in the province of La Union, Philippines. According to the 2020 census, it has a population of 40,846 people.

Santo Tomas is 230 kilometres (140 mi) from Metro Manila and 39 kilometres (24 mi) from San Fernando, the provincial capital.

The 18th and 19th centuries marked the active expansion of Ilocano territory. Scores of settlers from the Ilocos provinces pushed their way south so that by the end of the 19th century, Aringay was home to mostly Ilocanos, Ilocanized Pangasinenses, and Pangasinenses still speaking their native language. On December 22, 1941, units of the 192nd and 194th Tank Battalion of the United States Army Forces in the Far East engaged the Imperial Japanese Army's 4th Tank Regiment in Damortis, and lost with the capture of the Commanding Officer Lt. Ben R. Morin. This was the first time that the United States Army had a tank-to-tank battle. The armored battalions of the USAFFE fought continuously until during the Invasion of the Philippines, until April 7, 1942, two days before the Fall of Bataan.

Santo Tomas is politically subdivided into 24 barangays.  Each barangay consists of puroks and some have sitios.

Population census of Santo Tomas

Year	Pop.	±% p.a.
1903	5,446	—
1918	8,046	+2.64%
1939	10,352	+1.21%
1948	12,897	+2.47%
1960	14,929	+1.23%
1970	19,482	+2.69%
1975	21,341	+1.84%
1980	22,610	+1.16%
1990	27,352	+1.92%
1995	28,192	+0.57%
2000	31,204	+2.20%
2007	33,604	+1.03%
2010	35,999	+2.54%
2015	39,092	+1.58%
2020	40,846	+0.87%
Source: Philippine Statistics Authority

In the 2020 census, the population of Santo Tomas, La Union, was 40,846 people, with a density of 640 inhabitants per square kilometre or 1,700 inhabitants per square mile.

Poverty incidence of Santo Tomas

10 20 30 40 2006 33.40 2009 22.71 2012 12.28 2015 7.52 2018 3.37 2021 10.54 Source: Philippine Statistics Authority

Santo Tomas, belonging to the second congressional district of the province of La Union, is governed by a mayor designated as its local chief executive and by a municipal council as its legislative body in accordance with the Local Government Code. The mayor, vice mayor, and the councilors are elected directly by the people through an election which is being held every three years.

The Pamahalaang Bayan (Municipal Town Hall) is located on top of a hill.

Members of the Municipal Council
(2019–2022)

Position	Name
Congressman	Sandra Y. Eriguel
Mayor	Severino C. Carbonell
Vice-Mayor	Winnie N. Doctolero
Councilors	Carlito M. Dela Cruz Jr.
	Anthony M. Villanueva
	Aldreyn S. Cabico
	Celiaflor M. Bejar
	Noel G. Basi
	Leonor J. Tagubat
	Lorenzo R. Medina Jr.
	Vilea R. Capinpin

Santo Tomas' coastal areas are suitable for fishing. Local cuisine includes Damortis dried fish (daing stalls along the national highway), puto, Bibingka, Nilatekan, and Patopat.

The town holds the Daing Festival every April 20 and an annual town Fiesta every April 24 and 25.

Santo Thomas contains part of the Agoo–Damortis Protected Landscape and Seascape. In 2002, a plan to create a 10 hectare BFAR Mariculture Park within the town was launched.

Santo Thomas is a DENR-designated Regional Center for Inland Fisheries Research and contains an Institute of Fisheries. The town's "Nutri-Enriched Seaweed Noodles" earned first place in the Aquatic Technology Competition and Marketplace, Phil. Council Aquaculture and Marine Research and Development on January 28, 2010.

The barangay of Damortis is known as the 'Tabo-an of the North’ because of its priceless 'danggit' (often associated with the small malaga), the dalag-baybay, espada, sapsap, pusit, turay, dilis, and shrimp, a local fish, 1 foot basasong, dried bangus (milkfish), patis (fish sauce), alamang, and bagoong.

Religion plays an important role in the town's culture. The patron saint of the town fishermen is Senora Virgen del Mar Cautiva (Virgin of the Sea), whose Feast Day is celebrated every 26 April) at Poblacion.

One of Santo Tomas' cultural icons is the 1785 Holy Guardian Angels Parish Church, which celebrates the Patronal Fiesta on October 2. Its Parish Priests are Father Raul S. Panay and Fr. Emmanuel Bahiwag under the Vicariate of St. Francis Xavier under Vicar Forane, Fr. Joel Angelo Licos, under the jurisdiction of the Roman Catholic Diocese of San Fernando de La Union (Latin: Dioecesis Ferdinandopolitanus ab Unione, Suffragan of Lingayen – Dagupan), a diocese of the Latin Church of the Roman Catholic Church in the Philippines. The diocese was established in 1970 from the Archdiocese of Nueva Segovia.

In 1845, Padre Santiago Romero, Kura Paroko's carved three religious statues for the Church out of devotion to the "Virgin of the Rosaries". The statues depicted the Blessed Mother, St. Michael the Archangel, and the Holy Guardian Angels (patron of the Church). "Matutina" through the China Sea is held yearly on July, where the three images are inserted in three boxes and delivered to Santo Tomas by sailboat. In Bolinao, Pangasinan, Jolo pirates seized the "Matutina" and threw the three boxes of the statues into the sea, after severing the left forearm of the Virgin Mary. Although two of the boxes sank, the Virgin's allegedly remained dry and floated to the parish priest of Santo Tomas. The surviving statue was enthroned at the Church on July 19, 1845, amid reports of miracles, conversions, and healing. Augustinian friar Padre Lorenzo Rodriguez created a replacement arm for the statue out of gold and then a second out of ivory. Today, the ivory arm is displayed on the statue, fastened to it with string.

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  Town hall
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  View of downtown from Town Hall hill top
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  The Town Plaza
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  St. Mary of the Sea Academy

• La Union Website Archived 2012-07-10 at the Wayback Machine
• Philippine Standard Geographic Code
• Philippine Census Information
• Local Governance Performance Management System