As of the 2000 census, there were 404 people, 154 households, and 119 families residing in the township.
The population density was . There were 263 housing units at an average density of 17.5/sq mi (6.8/km<sup>2</sup>).
The racial makeup of the township was 99.75% White, and 0.25% from two or more races. Hispanic or Latino of any race were 0.25% of the population.
There were 154 households, out of which 32.5% had children under the age of eighteen living with them; 64.3% were married couples living together, 9.1% had a female householder with no husband present, and 22.7% were non-families. 19.5% of all households were made up of individuals, and 7.8% had someone living alone who was sixty-five years of age or older.
The average household size was 2.62 and the average family size was 2.92.
The township median age of thirty-nine years was slightly less than the county median age of forty years. The distribution by age group was 24.5% of residents who were under the age of eighteen, 5.4% who were aged eighteen to twenty-four, 30.7% who were aged twenty-five to forty-four, 25.5% who were aged forty-five to sixty-four, and 13.9% who were sixty-five years of age or older.
For every one hundred females, there were 98.0 males. For every one hundred females who were aged eighteen or older, there were 108.9 males.
The median income for a household in the township was $32,083, and the median income for a family was $40,469. Males had a median income of $31,250 compared with that of $26,250 for females.
The per capita income for the township was $22,784.
Approximately 11.1% of families and 11.8% of the population were living below the poverty line, including 11.0% of those who were under the age of eighteen and 3.8% of those who were aged sixty-five or older.
Education
- Karns City Area School District - public schools
- Karns City High School in neighboring Butler County
Recreation
A portion of the Pennsylvania State Game Lands Number 105 is located in Perry Township, at the confluence of Birch Run with the Allegheny River.