Tranquillity is a census-designated place (CDP) in Fresno County, California, United States. The population was 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).
As of the census of 2000, there were 813 people, 236 households, and 193 families residing in the CDP. The population density was 1,294.0 people per square mile (498.3/km²). There were 249 housing units at an average density of 396.3/sq mi (152.6/km²). The racial makeup of the CDP was 48.83% White, 0.74% Black or African American, 1.72% Native American, 3.69% Asian, 42.07% from other races, and 2.95% from two or more races. 64.94% of the population were Hispanic or Latino of any race.
There were 236 households out of which 44.5% had children under the age of 18 living with them, 66.5% were married couples living together, 10.2% had a female householder with no husband present, and 17.8% were non-families. 15.7% of all households were made up of individuals and 7.6% had someone living alone who was 65 years of age or older. The average household size was 3.44 and the average family size was 3.82.
In the CDP the population was spread out with 33.6% under the age of 18, 9.6% from 18 to 24, 25.6% from 25 to 44, 21.9% from 45 to 64, and 9.3% who were 65 years of age or older. The median age was 30 years. For every 100 females there were 114.5 males. For every 100 females age 18 and over, there were 101.5 males.
The median income for a household in the CDP was $42,857, and the median income for a family was $60,208. Males had a median income of $29,250 versus $17,222 for females. The per capita income for the CDP was $13,128. About 12.2% of families and 7.9% of the population were below the poverty line, including 5.2% of those under age 18 and 17.7% of those age 65 or over.