San Carlos is the 10th canton of the province of Alajuela in Costa Rica. With an area of.3347.98 km², it is the largest canton of the 82 that make up the country, surpassing in size the provinces of Cartago and Heredia, as well as the most developed and main axis of the Huetar Norte Region. It is divided into 13 districts. It borders on the north with the Republic of Nicaragua, on the west with the cantons of Los Chiles, Guatuso, Tilarán and San Ramón, on the south with the cantons of San Ramón, Zarcero and Valverde Vega, and on the east with the cantons of Río Cuarto and Sarapiquí. It was founded on September 26,1911. Its head is Quesada.
According to the 2011 National Census, the population of the canton was 163,745 inhabitants, of which 14.4% were born abroad. The same census highlights that there were 44,966 occupied homes, of which 61.1% were in good condition and there were problems of overcrowding in 6.5% of the houses.47.4% of its inhabitants lived in urban areas. According to the projection of the INEC as of June 30,2018, the population of San Carlos was 194,207 inhabitants and the population of Ciudad Quesada was 44,933 inhabitants. Among other data, the literacy level of the canton is 95.7%, with an average schooling of 7.0 years. For the year 2012, it had a human development index of 0.790 according to the United Nations Development Program.
Because of its extensive plains, its high rainfall and its fertile soil, San Carlos is one of the most productive economic zones of Costa Rica. In its wide territory all kinds of agricultural activities are carried out: extension livestock, fattening, production of milk and derivatives. Sugarcane, pineapple, citrus, tubers, basic grains and many others are grown. The presence in the district of La Fortuna of the Arenal Volcano, an active stratovolcano almost perfect cone that stands alone at 1,670 meters above sea level on land, makes it one of the four most visited tourist destinations in Costa Rica by nationals and foreigners. Lake Arenal, an artificial reservoir located at the foot of the volcano, between San Carlos and Tilarán, is the main source of hydroelectric power production in the country. For these reasons, San Carlos is known as the "generous and progressive" canton of Costa Rica.