Fayette County was created on September 26, 1783, from part of Westmoreland County and named after the Marquis de Lafayette. Its county seat is Uniontown.
As of the census of 2000, there were 148,644 people, 59,969 households, and 41,198 families residing in the county. The population density was 188 people per square mile (73/km²). There were 66,490 housing units at an average density of 84 per square mile (32/km²). The racial makeup of the county was 95.30% White, 3.51% Black or African American, 0.11% Native American, 0.22% Asian, 0.01% Pacific Islander, 0.11% from other races, and 0.73% from two or more races. 0.38% of the population were Hispanic or Latino of any race. 19.8% were of German, 13.2% Italian, 11.4% Irish, 9.2% American, 8.4% Polish, 7.9% English and 6.6% Slovak ancestry according to Census 2000.
There were 59,969 households out of which 28.70% had children under the age of 18 living with them, 51.80% were married couples living together, 12.40% had a female householder with no husband present, and 31.30% were non-families. 28.00% of all households were made up of individuals and 14.50% had someone living alone who was 65 years of age or older. The average household size was 2.43 and the average family size was 2.96.
In the county, the population was spread out with 22.70% under the age of 18, 7.70% from 18 to 24, 27.20% from 25 to 44, 24.20% from 45 to 64, and 18.10% who were 65 years of age or older. The median age was 40 years. For every 100 females there were 91.80 males. For every 100 females age 18 and over, there were 87.60 males.
A study released in 2009 by PathWays PA, in partnership with the Pennsylvania Department of Labor and Industry, found that 35% of families in Fayette County were economically distressed, that is, failing to earn a wage that would adequately provide food, shelter, child care, health care, and other basic necessities.