Pen Argyl is a borough in Northampton County, Pennsylvania, 18 miles (29 km) north of Easton, in the Lehigh Valley region of the state. It is part of Pennsylvania's Slate Belt.
In 1900, 2,784 people lived here, and in 1910, 3,967 people were at home in Pen Argyl. The population was 3,615 as of the 2000 census.
As of the censusGR2 of 2000, there were 3,615 people, 1,427 households, and 1,003 families residing in the borough. The population density was 1,004.1/km² (2,603.9/mi²). There were 1,506 housing units at an average density of 418.3/km² (1,084.8/mi²). The racial makeup of the borough was 97.81% White, 0.47% African American, 0.11% Native American, 0.55% Asian, 0.25% from other races, and 0.80% from two or more races. Hispanic or Latino of any race were 1.22% of the population.
There were 1,427 households out of which 36.7% had children under the age of 18 living with them, 53.7% were married couples living together, 12.2% had a female householder with no husband present, and 29.7% were non-families. 24.5% of all households were made up of individuals and 12.6% had someone living alone who was 65 years of age or older. The average household size was 2.52 and the average family size was 3.01.
In the borough the population was spread out with 26.7% under the age of 18, 6.9% from 18 to 24, 31.0% from 25 to 44, 20.2% from 45 to 64, and 15.2% who were 65 years of age or older. The median age was 36 years. For every 100 females there were 91.1 males. For every 100 females age 18 and over, there were 86.9 males.
The median income for a household in the borough was $40,066, and the median income for a family was $47,935. Males had a median income of $32,596 versus $23,239 for females. The per capita income for the borough was $18,145. About 4.3% of families and 5.7% of the population were below the poverty line, including 5.7% of those under age 18 and 8.9% of those age 65 or over.
The Borough is served by the Pen Argyl Area School District.