Río San Juan is a department in Nicaragua. It was formed in 1957 from parts of Chontales and Zelaya departments. It covers an area of 7,473 km² and has a population of 95,500 (2005 census). The capital is San Carlos. The Department also includes the Solentiname Islandsarchipelago and the San Juan River, after which it is named. Trinidad, in Río San Juan, is the most southerly point in Nicaragua.