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.

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.

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.

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.

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.

The municipality is bordered by the province of Ilocos Norte by Badoc and Nueva Era to the north, and Cabugao to the south.