Osa is the number 5 canton of the province of Puntarenas, on the Pacific coast of Costa Rica. It is located in the southeast of the country, in the Brunca Region. It has an area of 1930.24 km², which makes it the sixth largest canton in the country, and the second largest in the province of Puntarenas. It is bordered to the north by the cantons of Pérez Zeledón and Buenos Aires, to the southeast by the canton of Golfito and Golfo Dulce, and to the west by the Pacific Ocean. Its foundation dates from June 26,1914. It is divided into 6 districts. Its head is Ciudad Cortés, also known as Puerto Cortés.
According to the 2011 National Census, the population of the canton was 29,433 inhabitants, of which 4.1% were born abroad. The same census highlights that there were 8,904 occupied homes, of which 43.2% were in good condition and there were problems of overcrowding in 6.3% of the houses.38.0% of its inhabitants lived in urban areas. Among other data, the literacy level of the canton is 95.3%, with an average schooling of 6.8 years. Its economy is based on tourism, agro-industry and commerce. Through Palmar Norte pass roads like the Inter-American Highway that connects Osa to the south with Golfito, Corredores and Paso Canoas, and to the north with Buenos Aires of Puntarenas. It also passes the important route 34, known as Carretera Costanera, which connects with San Isidro del General and the capital of the country San José.
The name of the canton is in honor of the Cacique Osa, who reigned the Amerindians Terras, who in the beginnings of the Conquest lived in the area near the coast, which in documents of 1563 is cited as Golfo Dosa, now Golfo Dulce. In Osa is located the Térraba-Sierpe mangrove swamp, one of the most important in Costa Rica, as well as the Ballena marine national park and the wild refuge of the island of Caño. There are also four archaeological sites containing pre-Columbian stone spheres, which have been declared a World Heritage Site by Unesco. In 2017, Osa became the first canton in Costa Rica to eliminate plastic from its shops, restaurants, bars and other places, replacing them with other biodegradable products based on bamboo, cloth, starches and cereals.