San Carlos is the name of the 10th canton in the province of Alajuela in Costa Rica. The canton covers an area of 3,347.98 square kilometres, making it the largest canton in the country. The capital city of the canton is Ciudad Quesada, which is also known as San Carlos. The canton encompasses a major portion of the Llanura de San Carlos (San Carlos Plain), a wide expanse on the Caribbean side of the Cordillera Central (Central Mountain Range). San Carlos reaches north to the border of Nicaragua, east to the province of Heredia, west to the province of Guanacaste, and south into the heights of the Cordillera.