According to the United States Census Bureau, the township has a total area of 39.8 square miles (103 km2), all of it land. Fayette Township is bordered by Mifflin and Snyder Counties to the north, Monroe Township to the east, Delaware and Walker Townships to the south and Fermanagh Township to the west.
Cocolamus Mennonite Church in Bunkertown
As of the census of 2000, there were 3,252 people, 1,219 households, and 936 families residing in the township. The population density was 81.8 people per square mile (31.6/km²). There were 1,372 housing units at an average density of 34.5/sq mi (13.3/km²). The racial makeup of the township was 98.77% White, 0.34% African American, 0.06% Native American, 0.12% Asian, 0.15% Pacific Islander, 0.28% from other races, and 0.28% from two or more races. Hispanic or Latino of any race were 0.71% of the population.
There were 1,219 households, out of which 33.9% had children under the age of 18 living with them, 67.4% were married couples living together, 5.8% had a female householder with no husband present, and 23.2% were non-families. 20.5% of all households were made up of individuals, and 10.2% had someone living alone who was 65 years of age or older. The average household size was 2.67 and the average family size was 3.08.
In the township the population was spread out, with 27.3% under the age of 18, 8.0% from 18 to 24, 27.7% from 25 to 44, 23.0% from 45 to 64, and 14.0% who were 65 years of age or older. The median age was 36 years. For every 100 females, there were 100.2 males. For every 100 females age 18 and over, there were 96.4 males.
The median income for a household in the township was $30,653, and the median income for a family was $35,884. Males had a median income of $29,679 versus $21,362 for females. The per capita income for the township was $16,548. About 7.0% of families and 9.5% of the population were below the poverty line, including 11.7% of those under age 18 and 5.2% of those age 65 or over.