Santa Catalina, Ilocos Sur  ', officially the ', is a in the province of , . According to the , it has a population of people. With an area of , it is the smallest municipality in the province and the only municipality in Ilocos Sur which has an urban status for all its barangays based on National Statistical Coordination Board (NSCB). The feast of the town is celebrated every 25th day of November to celebrate the feast day of Saint Catherine of Alexandria (the town's patron saint). When the Augustinians were busy with the Christianization of the Ilocos Region, a group of missionaries sailed westward through the river known as "El Mestizo" to the place now called Santa Catalina. They were also looking for fresh water, since the area where he landed yielded only salty water. When they finally found a fresh water spring up north, and were busy quenching their thirst, some of them saw an image of a beautiful lady near the place where he drank, which disappeared after a few minutes. One of them recognized the image as that of Saint Catherine of Alexandria. The Augustinians returned to Villa Fernandina (Vigan) and reported this matter to their superiors. This resulted in the construction of a church in the town with Saint Catherine of Alexandria as the patron saint. It was also declared that "Santa Catalina" be the name of the town. A replica of the cross once planted by Salcedo and his party—to signify that the Spanish has conquered the area—stands near the entrance to the municipality. Santa Catalina is politically subdivided into 9 barangays. It has 3 sitios, namely:  In the , the population of Santa Catalina, Ilocos Sur, was people, with a density of . As of February 2006, Santa Catalina with a poverty incidence of 7.9 percent and Vigan City with a poverty incidence of 8.6 percent, are the top two municipalities/cities with lowest poverty incidences in Ilocos Sur, and for the entire northern Luzon. This is among the results of the Poverty Mapping Project implemented by the National Statistical Coordination Board (NSCB) with funding assistance from the World Bank ASEM Trust Fund in response to the increasing demand for local level poverty estimates. A total of 696.5888 hectares or 74.581% of the total land area of Santa Catalina is utilized for crop production. Croplands are found in every barangay.