Perry County, originally part of Cumberland County, was created in 1820 in part because residents did not want to travel over the mountain to Carlisle (the county seat of Cumberland County). Perry County's county seat is New Bloomfield. It was created on March 22, 1820, and was named after Oliver Hazard Perry, hero of the War of 1812, who had recently died.
The village of Green Park in northeastern Tyrone Township serves as the county's midpoint between the Conococheague Mountain in the west and the Susquehanna River to the east. As of August 2005, Perry County was one of only two counties in Pennsylvania without a permanent traffic light. However, since then a traffic light has been approved for Marysville and may be installed during 2009.
As of the census of 2000, there were 43,602 people, 16,695 households, and 12,320 families residing in the county. The population density was 79 people per square mile (30/km²). There were 18,941 housing units at an average density of 34 per square mile (13/km²). The racial makeup of the county was 98.54% White, 0.43% Black or African American, 0.12% Native American, 0.15% Asian, 0.01% Pacific Islander, 0.21% from other races, and 0.54% from two or more races. 0.69% of the population were Hispanic or Latino of any race. 45.8% were of German, 16.4% American, 7.8% Irish and 5.0% English ancestry according to Census 2000. 96.8% spoke English and 1.2% Spanish as their first language.
There were 16,695 households out of which 33.2% had children under the age of 18 living with them, 61.6% were married couples living together, 7.8% had a female householder with no husband present, and 26.20% were non-families. 21.7% of all households were made up of individuals and 9.30% had someone living alone who was 65 years of age or older. The average household size was 2.58 and the average family size was 3.01. There is also a high population of Amish.
In the county, the population was spread out with 25.5% under the age of 18, 7.4% from 18 to 24, 29.8% from 25 to 44, 25.1% from 45 to 64, and 12.3% who were 65 years of age or older. The median age was 38 years. For every 100 females there were 98.4 males. For every 100 females age 18 and over, there were 96.9 males.