Rosario, officially the Municipality of Rosario, is a municipality in the province of Northern Samar, Philippines. According to the 2020 cens…Rosario, officially the Municipality of Rosario, is a municipality in the province of Northern Samar, Philippines. According to the 2020 census, it has a population of 10,949 people. It is bordered in the west by Lavezares and Victoria to the south. Its coastal area is protected as part of the Biri Larosa Protected Landscape and Seascape.