Sinait, officially the Municipality of Sinait (Ilocano: Ili ti Sinait; Filipino: Bayan ng Sinait), is a 3rd class municipality in the province of Ilocos Sur, Philippines. According to the 2020 census, it has a population of 25,998 people.

Before Magellan discovered the Philippines in 1521, the locality was only a small village of little over a hundred natives who were called "Tirongs." By nature, these primitive inhabitants were sea-faring warlike. In their fast and picturesque sailboats, they traveled to adjoining and distant places, most particularly to settlements and villages along the Ilocos Coast in Ilocos Norte, Ilocos Sur, La Union, Pangasinan and even Zambales. In those adventures, the “Tirongs “ always challenged the people encountered to tribal wars and fought small battles against them. Often, those sturdy and brave natives came out victorious. Even in their daily chores, those people showed their ferocious characteristics. When the renowned Iberians came, Juan de Salcedo was sent to explore and colonized the Ilocos territory during the early years of the Spanish regime, he found the “Tirongs” of Sinait in apogee of the social state. Small battles were daily occurrence so that in the year 1535, when the locality was organized and established as a “Pueblo.” Salcedo named the new community as “SIN-NAIT”, a word in the local tongue which means “CONTEST”. As a pueblo, Sinait embraced and included in its territorial limit such as distant places as "Rancheria de Paur," now the Municipality of Nueva Era in Ilocos Norte and Southern barrios of Badoc of the same Province. The vast territory, however, was reduced to present 78 square kilometers. In the year 1575, the natives fully realized the hardships of pronouncing the term “Sin-nait” and to go away with the trouble, Salcedo declared that one of the letter “N” be dropped. Since then, this Municipality has been called “Sinait”. Nevertheless, it was only in 1913 when the same was “deeded” by the government upon the initiative of the late Don Calixto Cabacungan so that the Municipality Council enacted a resolution to that effect, that Sinait was adopted as official name of the community to which said resolution was duly approved by the Provincial board of Ilocos Sur and by the Defunct Philippine Legislature.

Sinait houses the Sanctuary of the Miraculous Statue of the Black Nazarene (El Santo Cristo Milagroso), fondly called by its residents as "Apo Lakay," and a treasure of Ilocandia. History traces the life-sized statue to Nagasaki, Japan. It was probably sent floating in the sea by missionaries operating in secret in Japan (for fear of persecution during the Tokugawa Bakufu). The box was found by local fishermen in the shores of Barangay Dadalaquiten Norte, on the boundary between Sinait and nearby Paguetpet (La Virgen Milagrosa), Badoc, in the year 1620, and fishermen from both towns carried it ashore. They found two statues inside the box—a statue of the Black Nazarene, and a statue of the Blessed Virgin Mary. According to legend, The fishermen from Sinait mysteriously were unable to move the statue of the Blessed Virgin Mary, but had no problems moving the Statue of the Black Nazarene. The fishermen from Badoc, however, were able to move the Statue of the Blessed Virgin Mary (later called the La Virgen Milagrosa) with ease, as they were unable to carry the image of the Black Nazarene. They took the statues to their respective towns and were venerated. In 1656, with a spreading devotion to the Santo Cristo Milagroso due to its miraculous powers, the Black Crucifix was taken to the capital town of Vigan, since an epidemic was raging there and through the devotion of the faithful, many got cured. Because of this, it is considered as an intercessor of all kinds of affliction and sickness. In 1660, because of the growing veneration to the image, the faithful begun the construction of a permanent edifice to house it. It took the people of Sinait eight years to construct the church with funds provides by the Spanish Audiencia. Today the landing site of Apo Lakay is marked by a chapel at Lugo Beach in Barangay Dadalaquiten Norte, and is a place of pilgrimage for devotees, as with the nearby chapel marking La Virgen Milagrosa's landing site.

It is the northernmost municipality of the province and is 36 kilometres (22 mi) from the provincial capital, Vigan, 46 kilometres (29 mi) from Laoag, and 441 kilometres (274 mi) from Manila. The municipality is bordered by the province of Ilocos Norte by Badoc and Nueva Era to the north, and Cabugao to the south.

Sinait is politically subdivided into 44 barangays.  Each barangay consists of puroks and some have sitios.

Population census of Sinait

Year Pop. ±% p.a. 1903 9,157 —     1918 12,335 +2.01% 1939 11,722 −0.24% 1948 12,015 +0.27% 1960 15,170 +1.96%	Year Pop. ±% p.a. 1970 16,429 +0.80% 1975 17,952 +1.79% 1980 19,050 +1.19% 1990 21,779 +1.35% 1995 22,608 +0.70%	Year Pop. ±% p.a. 2000 24,070 +1.35% 2007 24,896 +0.47% 2010 25,427 +0.77% 2015 25,640 +0.16% 2020 25,998 +0.27%
Source: Philippine Statistics Authority

In the 2020 census, Sinait had a population of 25,998. The population density was 400 inhabitants per square kilometre (1,000/sq mi).

Poverty incidence of Sinait

5 10 15 20 2006 16.70 2009 18.68 2012 20.00 2015 12.24 2018 5.64 2021 18.28 Source: Philippine Statistics Authority

As major producer of Garlic, Sinait is also known as the Garlic Center of the North.

• Sinait Public Market - On certain days garlic from the municipality and even the neighboring municipalities of Badoc and Pinili in neighboring Ilocos Norte are traded here.
• Barangay Pug-os/Dean Leopoldo Yabes - Barangay Pug-os was renamed as Barangay Dean Leopoldo Yabes, in honor of the Ilocano writer and dean from the University of the Philippines who once lived in Sinait.
• Cabangtalan (Imelda's Cove) - Features white sand beaches. It is located on the way to Barangay Dadalaquiten Norte and Paguetpet (Badoc).
• Basilica of Saint Nicholas de Tolentino and Shrine of El Santo Cristo Milagroso - A Roman Catholic church, and a minor basilica, that houses the Miraculous Statue of the Black Nazarene (El Santo Cristo Milagroso) or "Apo Lakay." On May 3, 2021, Archbishop Marlo Peralta of the Archdiocese of Nueva Segovia announced that Pope Francis elevated the church to the rank of minor basilica during a Mass. On February 16, 2022, it was officially declared as a minor basilica in a Eucharistic Celebration presided by the Apostolic Nuncio to the Philippines Archbishop Charles John Brown and concelebrated by Archbishop of Nueva Segovia Marlo Mendoza Peralta and Archbishop of Lingayen-Dagupan Socrates Villegas with Archbishop of Manila Cardinal Jose Fuerte Advincula as the homilist, and also attended by Archbishop-emeritus of Cotabato Cardinal Orlando Beltran Quevedo and six other bishops from Northern Luzon.
• Barangay Dadalaquiten Norte - The landing place of the Miraculous Statue of the Black Nazarene in 1620, close to the landing place of the La Virgen Milagrosa in neighboring Paguetpet, Badoc, Ilocos Norte.
• Libunao Protected Landscape - A protected watershed area in Barangay Nagcullooban.
• Sinait National High School - One of the largest secondary schools in Ilocos Sur.
• Calanutian - Homeplace of Inez Cannoyan the wife of Lam-Ang in the fictional Ilocano Story Biag ni Lam-Ang
• Lugo Beach - A summer destination located at Dadalaquiten Norte, where the Dadalaquiten Floating Cottages are found. The place where the Santo Cristo Milagroso was carried ashore when it was found (with the La Virgen Milagrosa).
• Cabulalaan Hills - A hiking destination.

Sinait, belonging to the first congressional district of the province of Ilocos Sur, 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.

Members of the Municipal Council
(2022–2025)

Position	Name
Congressman	Ronald V. Singson
Mayor	Glenn B. Guzman
Vice-Mayor	Shee-an C. Guzman
Councilors	Romel P. Dayoan
	Marlowrie I. Remolacio
	Marlon B. Ines
	King Dave V. Guzman
	Jojo Q. Yoro
	Wilhelmina R. Ibanez
	Jaco Rafael C. Agdeppa
	Leopoldo Florentino D. Rosete

• Pasyalang Ilocos Sur
• Philippine Standard Geographic Code
• Philippine Census Information
• Sinait National High School - Official Website
• Local Governance Performance Management System