Tranquillity is a census-designated place (CDP) in Fresno County, California, United States. The population was 799 at the 2010 census, down from 813 at the 2000 census. Tranquillity High School is the only high school in Tranquillity. Tranquillity is located 10 miles (16 km) southeast of Mendota, at an elevation of 164 feet (50 m).
According to the United States Census Bureau, the CDP has a total area of 0.6 square miles (1.6 km²), all of it land.
The first post office opened in Tranquillity in 1910.