Charleroi is a borough in Washington County, Pennsylvania, along the Monongahela River, 25 miles south of Pittsburgh. Charleroi was settled in 1890 and incorporated in 1891. The population in 1900 stood at 5,930; in 1910, 9,615; in 1920, 11,516, and in 1940, 10,784. The population was 4,871 at the 2000 census.
There has been a large-scale cessation of industrial activities in the region. The decrease in the population is associated with the decline of the steel-making industry in the "Mon Valley" which extends from Charleroi to the mouth of the Monongahela at Pittsburgh.
According to the United States Census Bureau, the borough has a total area of 0.9 square miles (2.2 km²), of which, 0.8 square miles (2.0 km²) of it is land and 0.1 square miles (0.2 km²) of it is water. The total area is 10.47% water.
There were 2,258 households out of which 22.3% had children under the age of 18 living with them, 35.5% were married couples living together, 13.7% had a female householder with no husband present, and 46.5% were non-families. 41.8% of all households were made up of individuals and 21.9% had someone living alone who was 65 years of age or older. The average household size was 2.11 and the average family size was 2.88.
In the borough the population was spread out with 20.5% under the age of 18, 7.1% from 18 to 24, 27.1% from 25 to 44, 20.2% from 45 to 64, and 25.0% who were 65 years of age or older. The median age was 41 years. For every 100 females there were 81.4 males. For every 100 females age 18 and over, there were 77.1 males.
The median income for a household in the borough was $23,593, and the median income for a family was $31,699. Males had a median income of $30,093 versus $23,873 for females. The per capita income for the borough was $13,752. About 16.1% of families and 21.3% of the population were below the poverty line, including 36.2% of those under age 18 and 13.7% of those age 65 or over.