Washington County is one of three counties in the Hagerstown-Martinsburg, MD-WV Metropolitan Statistical Area. Due to commuting patterns, a high growth rate, and close proximity, Washington County is also often considered, though not officially designated a part of the Washington-Baltimore-Northern Virginia, DC-MD-VA-WV Combined Statistical Area.
As of the census of 2000, there were 131,923 people, 49,726 households, and 34,112 families residing in the county. The population density was 288 people per square mile (111/km²). There were 52,972 housing units at an average density of 116 per square mile (45/km²). The racial makeup of the county was 89.71% White or Caucasian, 7.77% Black or African American, 0.18% Native American, 0.80% Asian, 0.04% Pacific Islander, 0.46% from other races, and 1.04% from two or more races. 1.19% of the population were Hispanic or Latino of any race. 32.1% were of German, 21.4% American, 8.8% Irish and 8.4% English ancestry according to Census 2000.
There were 49,726 households out of which 31.30% had children under the age of 18 living with them, 54.00% were married couples living together, 10.70% had a female householder with no husband present, and 31.40% were non-families. 26.00% of all households were made up of individuals and 11.10% had someone living alone who was 65 years of age or older. The average household size was 2.46 and the average family size was 2.96.
In the county the population was spread out with 23.40% under the age of 18, 8.10% from 18 to 24, 31.30% from 25 to 44, 23.00% from 45 to 64, and 14.20% who were 65 years of age or older. The median age was 37 years. For every 100 females there were 104.50 males. For every 100 females age 18 and over, there were 104.00 males.
The median income for a household in the county was $40,617, and the median income for a family was $48,962. Males had a median income of $34,917 versus $24,524 for females. The per capita income for the county was $20,062. About 7.00% of families and 9.50% of the population were below the poverty line, including 12.30% of those under age 18 and 9.50% of those age 65 or over.