San Mariano, officially the Municipality of San Mariano; Ilocano: Ili ti San Mariano; Tagalog: Bayan ng San Mariano), is a municipality in the province of Isabela, Philippines. According to the 2020 census, it has a population of 60,124 people.

According to legend, it was first named Angela in reference to her husband, Mariano Kalingog, whose family was one of the foremost settlers of the place. Angela drowned while she was washing clothes along the Pinacanauan River, bringing grief to her husband, who also died some years later. Since then, the village was known as San Mariano.

The area covered by San Mariano was part of a wide region that stretched from the edge of Ilagan to the Sierra Madre mountains called Catalangan, derived from the word talang (pine), possibly due to that tree's abundance in the Sierra Madre. It was officially established by the Spaniards as a mission in 1755.

San Mariano was once a barrio of Ilagan, the capital of Isabela.

In 1920, by virtue of Executive Order 25, San Mariano became a Municipal district, and with the passage of Philippines Legislature Act No. 3416 dated December 7, 1927, it was made a distinct and regular municipality.

During those years, there was an influx of migrants coming from the provinces of Ilocos, Cagayan, and Pangasinan. These new settlers formed communities on agricultural lands on which they grew corn and other crops such as rice, root crops, different kinds of vegetables and bananas.

When the German naturalist Carl Semper hiked the Sierra Madre mountains in May 1860, he observed early inhabitants who are known today as the Kalingas. He described the said group as a typical Filipino “cultural minority” who grew their own food, practiced their own religious rites, smithed their own tools, decorated their own artifacts with distinctive designs and traded forest products for metal and salt.

On the Pacific side of the mountains, Semper saw the “Negritos” and concluded that they were new arrivals because he observed no “Kalinga-Negrito” mestizos among them. They inhabited the forest close to the “Kalinga” settlements and showed up with games in seasonal periods to barter for agricultural products. Years later, some sociologists noted that there were inter-marriages entered into between these tribes.

These natives, however, were out-numbered by the mestizos or the “Ibanag-Kalinga,” the Ibanags and Ilocanos with a ratio of about four to one. These settlers tilled permanent farms at the present-day Barangays of Disulap and Minanga.

There was also an influx of several groups from the Bicol and Tagalog regions during the logging concession boom. The continuing acculturation of these groups brought about social changes in the locality. The once verdant forest slowly became barren and denuded with the ceaseless illegal logging and kaingin system employed by the local people and new migrants. When the national government decided to impose a total log ban, the ethnic groups decided to settle in the remote areas of the municipality to farm their lands. The Bicolanos and Tagalogs moved out.

San Mariano has a total land area of 146,950 hectares (363,100 acres).  It constitutes 13.78 percent of the total land area of the province, and is the province's largest and the country's third largest municipality. It is a suburb of Ilagan, the provincial capital.

The municipality lies in the eastern part of the province of Isabela. It is bounded on the north by the Ilagan, on the east by Palanan, on the south by San Guillermo and on the west by Benito Soliven. It is approximately 404 kilometres (251 mi) from Metro Manila and 46 kilometres (29 mi) from Ilagan, the provincial capital.

San Mariano is politically subdivided into 36 barangays.  Each barangay consists of puroks while some have sitios.

Of the total land area of the municipality, built-up area constitutes 1,268 hectares or 0.86 percent with the Poblacion as the largest and most densely populated built-up area. Open grasslands occupy a total area of approximately 20,700 hectares representing about 14.09 percent. Generally, the open grasslands are flanked by either agricultural areas or forest areas. Vast forest areas of the municipality are mostly found at its eastern portion, which covers about 53.39 percent or an approximated area of 78,450.50 hectares. About 29,264 hectares or 19.91 percent are presently devoted to extensive agricultural activities with corn, rice and bananas as the major crops. Water bodies, including banks, buffer or salvage zones occupy an estimated 11.58 percent while existing roads and streets cover 2.17 percent of the municipality's total area.

Population census of San Mariano

Year	Pop.	±% p.a.
1918	1,486	—
1939	7,046	+7.69%
1948	8,365	+1.92%
1960	15,064	+5.02%
1970	20,227	+2.99%
1975	25,157	+4.47%
1980	31,839	+4.82%
1990	36,295	+1.32%
1995	37,861	+0.79%
2000	41,309	+1.89%
2007	44,718	+1.10%
2010	51,438	+5.23%
2015	55,370	+1.41%
2020	60,124	+1.63%
Source: Philippine Statistics Authority

In the 2020 census, the population of San Mariano, Isabela, was 60,124 people, with a density of 41 inhabitants per square kilometre or 110 inhabitants per square mile.

Poverty incidence of San Mariano

10 20 30 40 2006 29.80 2009 24.20 2012 30.61 2015 25.34 2018 23.09 2021 25.00 Source: Philippine Statistics Authority

As a municipality in the Province of Isabela, government officials in the provincial level are voted by the electorates of the town. The provincial government have political jurisdiction over local transactions of the municipal government.

The municipality of San Mariano 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.

Barangays are also headed by elected officials: Barangay Captain, Barangay Council, whose members are called Barangay Councilors. The barangays have SK federation which represents the barangay, headed by SK chairperson and whose members are called SK councilors. All officials are also elected every three years.

Members of the San Mariano Municipal Council
(2022-2025)

Position	Name
District Representative	Ed Christopher S. Go
Municipal Mayor	Edgar T. Go
Municipal Vice-Mayor	Dean Anthony G. Domalanta
Municipal Councilors	Marivic B. Sumisim
	Jerimar C. Miranda
	Nemo Nick A. Aggabao
	Girlie May G. Warren
	Susana P. Duca
	Sigrid Minette L. Miranda
	Kevin L. Pascual
	Florita Marietta T. Bartolome

San Mariano, belonging to the second legislative district of the province of Isabela, currently represented by Hon. Ed Christopher S. Go.

Leaders of Town	Date
Ferando Ampa	1924 - 1927
Placido Buensuceso	1927 - 1931
Eulogio Alejo	1931 - 1934
Elias Gabriel	1934 - 1945
Jose Miranda	1945 - 1947
Felicisimo Baua	1947 - 1963
Emilio Bueno	1964 - 1967
Jose Miranda	1967 - 1976
Carlos Dumelod	1976 to 1980
Deodoro Go	1980
Carlos Dumelod	December 1980 - 1986
Aristotle Claravall	1986 - 1987
Romulo S. Taggueg Jr.	1987 - 1988
Deodoro Go	1988 - 1995
Jesus C. Miranda	1995 - 2004
Edgar T. Go	2004 - 2013
Dean Anthony Domalanta	2013 - 2016
Edgar T. Go	2016–present

The Schools Division of Isabela governs the town's public education system. The division office is a field office of the DepEd in Cagayan Valley region. The office governs the public and private elementary and public and private high schools throughout the municipality.

• Municipal Profile at the National Competitiveness Council of the Philippines
• San Mariano at the Isabela Government Website
• Local Governance Performance Management System
• Philippine Standard Geographic Code
• Philippine Census Information
• Municipality of San Mariano
• San Mariano Website