Westtown Township is a township in Chester County, Pennsylvania, United States. The population was 10,827 at the 2010 census. County Bridge No. 148 was listed on the National Register of Historic Places in 1988. According to the United States Census Bureau, the township has a total area of 8.8 square miles (23 km2), of which 8.7 square miles (23 km2) is land and 0.04 square miles (0.10 km2), or 0.23%, is water.
As of the census of 2000, there were 10,352 people, 3,705 households, and 2,949 families residing in the township. The population density was 1,185.5 people per square mile (457.8/km²). There were 3,795 housing units at an average density of 434.6/sq mi (167.8/km²). The racial makeup of the township was 93.97% White, 2.59% African American, 0.07% Native American, 2.42% Asian, 0.01% Pacific Islander, 0.37% from other races, and 0.57% from two or more races. Hispanic or Latino of any race were 1.13% of the population.
There were 3,705 households out of which 38.7% had children under the age of 18 living with them, 70.6% were married couples living together, 6.9% had a female householder with no husband present, and 20.4% were non-families. 16.0% of all households were made up of individuals and 4.0% had someone living alone who was 65 years of age or older. The average household size was 2.78 and the average family size was 3.14.
In the township the population was spread out with 26.9% under the age of 18, 6.0% from 18 to 24, 28.9% from 25 to 44, 28.2% from 45 to 64, and 9.9% who were 65 years of age or older. The median age was 39 years. For every 100 females there were 96.0 males. For every 100 females age 18 and over, there were 93.1 males.
The median income for a household in the township was $85,049, and the median income for a family was $96,318. Males had a median income of $66,675 versus $43,482 for females. The per capita income for the township was $36,894. About 2.1% of families and 3.0% of the population were below the poverty line, including 1.7% of those under age 18 and 3.5% of those age 65 or over.