As of the census of 2000, there were 319,250 people, 130,687 households, and 84,293 families residing in the county. The population density was 358 people per square mile (138/km²). There were 144,686 housing units at an average density of 162 per square mile (63/km²). The racial makeup of the county was 96.63% White, 1.69% Black or African American, 0.09% Native American, 0.58% Asian, 0.01% Pacific Islander, 0.43% from other races, and 0.57% from two or more races. 1.16% of the population were Hispanic or Latino of any race. 22.2% were of Polish, 15.6% Italian, 13.8% Irish, 12.1% German and 5.3% Slovak ancestry according to Census 2000.
There were 130,687 households out of which 26.50% had children under the age of 18 living with them, 48.80% were married couples living together, 11.50% had a female householder with no husband present, and 35.50% were non-families. 31.30% of all households were made up of individuals and 16.00% had someone living alone who was 65 years of age or older. The average household size was 2.34 and the average family size was 2.95.
In the county, the population was spread out with 21.00% under the age of 18, 8.10% from 18 to 24, 27.20% from 25 to 44, 24.00% from 45 to 64, and 19.70% who were 65 years of age or older. The median age was 41 years. For every 100 females there were 93.00 males. For every 100 females age 18 and over, there were 89.50 males.
Luzerne Country is the only county in the United States with a plurality of citizens reporting Polish as their primary ancestry; the majority of Pennsylvanians report German or Pennsylvania Dutch.