St. Tammany Parish (French: Paroisse de Saint-Tammany) is a parish located in the U.S. state of Louisiana. As of the 2010 census, the population was 233,740, making it the fifth-most populous parish in Louisiana. The parish seat is Covington. The parish was founded in 1810.
According to the U.S. Census Bureau, the parish has a total area of 1,124 square miles (2,910 km), of which 846 square miles (2,190 km) is land and 279 square miles (720 km) (25%) is water. It is located to the north of Lake Pontchartrain.
At the 2000 census, there were 191,268 people, 69,253 households and 52,701 families residing in the parish. The population density was 224 per square mile (86/km²). There were 75,398 housing units at an average density of 88 per square mile (34/km²). The racial makeup of the parish was 87.03% White, 9.90% Black or African American, 0.43% Native American, 0.74% Asian, 0.03% Pacific Islander, 0.61% from other races, and 1.26% from two or more races. 2.48% of the population were Hispanic or Latino of any race. There were 69,253 households of which 39.30% had children under the age of 18 living with them, 61.40% were married couples living together, 11.00% had a female householder with no husband present, and 23.90% were non-families. 19.70% of all households were made up of individuals and 6.70% had someone living alone who was 65 years of age or older. The average household size was 2.73 and the average family size was 3.15.
Age distribution was 28.40% under the age of 18, 7.30% from 18 to 24, 29.90% from 25 to 44, 24.30% from 45 to 64, and 10.00% who were 65 years of age or older. The median age was 36 years. For every 100 females there were 96.10 males. For every 100 females age 18 and over, there were 92.40 males. The median household income was $47,883, and the median family income was $55,346. Males had a median income of $41,876 versus $25,996 for females. The per capita income for the parish was $22,514. About 7.60% of families and 9.70% of the population were below the poverty line, including 11.80% of those under age 18 and 10.10% of those age 65 or over.