Historically, structural iron, knit goods, and silk were manufactured in Slatington, and there were abundant slate quarries in the area.
Slatington was settled in 1738 and incorporated in 1864.
In 1737, Nicholas Kern was the first white settler in what would become Slatington. The Lenni-Lenape Native Americans were already living along "Warriors Path," which would become Route 873. Kern established a sawmill shortly after arriving. In 1756, Benjamin Franklin reported to Governor Morris that he had procured boards and timber from Kern's sawmill. In the 19th century two Welshman, who recognized its properties and importance from being used in Europe, discovered slate. A quarry was set up in 1845, and, in 1847, a factory was erected. In 1846, Slatington was incorporated into a Borough of Pennsylvania; its first Mayor was Robert McDowell.
As of the censusGR2 of 2000, there were 4,434 people, 1,743 households, and 1,190 families residing in the borough. The population density was 1,297.0/km² (3,354.6/mi²). There were 1,867 housing units at an average density of 546.1/km² (1,412.5/mi²). The racial makeup of the borough was 96.23% White, 1.42% African American, 0.20% Native American, 0.38% Asian, 0.02% Pacific Islander, 0.77% from other races, and 0.97% from two or more races. Hispanic or Latino of any race were 2.03% of the population.
There were 1,743 households out of which 35.7% had children under the age of 18 living with them, 48.7% were married couples living together, 13.9% had a female householder with no husband present, and 31.7% were non-families. 26.4% of all households were made up of individuals and 12.5% had someone living alone who was 65 years of age or older. The average household size was 2.51 and the average family size was 3.01.
In the borough the population was spread out with 27.1% under the age of 18, 7.5% from 18 to 24, 32.4% from 25 to 44, 19.7% from 45 to 64, and 13.3% who were 65 years of age or older. The median age was 36 years. For every 100 females there were 94.7 males. For every 100 females age 18 and over, there were 89.3 males.
The median income for a household in the borough was $36,531, and the median income for a family was $43,542. Males had a median income of $32,101 versus $23,796 for females. The per capita income for the borough was $16,189. About 10.6% of families and 12.3% of the population were below the poverty line, including 14.1% of those under age 18 and 10.1% of those age 65 or over.
The Borough is served by the Northern Lehigh School District.