According to the United States Census Bureau, the township has a total area of, of which, is land and is water. The township contains the following communities: Armbrust, Bovard, Carbon, Centerville, Darragh, Eastwood, Emmonston, Evanston, Fort Allen, Grapeville, Hannastown, Haydenville, High Park, Lincoln Heights, Luxor, Maplewood Terrace, Midway, Radebaugh, St. Clair, Stonevilla, Swede Hill, White Hill, and West Point City.
At the 2000 census there were 40,721 people, 15,997 households, and 11,597 families living in the township. The population density was 531.5 people per square mile. There were 16,799 housing units at an average density of 219.2/sq mi. The racial makeup of the township was 97.42% White, 1.11% Black or African American, 0.08% Native American, 0.84% Asian, 0.04% Pacific Islander, 0.11% from other races, and 0.40% from two or more races. Hispanic or Latino people of any race were 0.38%. Of the 15,997 households 28.4% had children under the age of 18 living with them, 61.8% were married couples living together, 7.8% had a female householder with no husband present, and 27.5% were non-families. 24.3% of households were one person and 11.7% were one person aged 65 or older. The average household size was 2.43 and the average family size was 2.89. The age distribution was 20.4% under the age of 18, 7.5% from 18 to 24, 26.5% from 25 to 44, 27.8% from 45 to 64, and 17.8% 65 or older. The median age was 42 years. For every 100 females, there were 93.2 males. For every 100 females age 18 and over, there were 90.1 males. The median household income was $42,288 and the median family income was $52,440. Males had a median income of $39,001 versus $25,838 for females. The per capita income for the township was $21,839. 6.0% of the population and 4.1% of families were below the poverty line. Out of the total population, 7.8% of those under the age of 18 and 7.0% of those 65 and older were living below the poverty line.
Hempfield Township is a major economic player in Westmoreland County. As the retail hub for Westmoreland County and the Laurel Highlands region in particular, it is home to the popular Westmoreland Mall, the third largest shopping and entertainment complex in the Pittsburgh Metropolitan Area. In addition, Greengate Centre serves as the area's largest big-box retail center. Several smaller shopping centers, well-known national retailers and restaurants can also be found in the township. Light industry can also be found within Hempfield Township including numerous industrial parks and facilities. RIDC Westmoreland straddles Hempfield and East Huntingdon townships.
2011 tornado
On March 23, 2011, a funnel cloud briefly appeared over the central area of Hempfield Township southwest of the city of Greensburg just around 4:45 PM and eventually touched down as an EF2 tornado, causing widespread damage to scores of homes in the West Hempfield area as well as the Fort Allen neighborhood and in neighboring Sewickley Township. Hempfield Area High School was especially impacted with major damage to the auditorium's roof and stadium, as was nearby Harrold Middle School.
