Jefferson County is the most populous county in the Louisville/Jefferson County, KY–IN Metropolitan Statistical Area.
As of the census of 2000, there were 693,604 people, 287,012 households, and 183,113 families residing in the county. The population density was 1,801 per square mile (695 /km). There were 305,835 housing units at an average density of 794 per square mile (307 /km). The racial makeup of the county was 77.38% White, 18.88% Black or African American, 0.22% Native American, 1.39% Asian, 0.04% Pacific Islander, 0.68% from other races, and 1.42% from two or more races. 1.78% of the population were Hispanic or Latino of any race.
There were 287,012 households out of which 29.60% had children under the age of 18 living with them, 45.20% were married couples living together, 14.70% had a female householder with no husband present, and 36.20% were non-families. 30.50% of all households were made up of individuals and 10.30% had someone living alone who was 65 years of age or older. The average household size was 2.37 and the average family size was 2.97.
In the county the population was spread out with 24.30% under the age of 18, 8.90% from 18 to 24, 30.40% from 25 to 44, 22.80% from 45 to 64, and 13.50% who were 65 years of age or older. The median age was 37 years. For every 100 females there were 91.60 males. For every 100 females age 18 and over, there were 87.60 males.
The median income for a household in the county was $43,789 (2005), and the median income for a family was $49,161. Males had a median income of $36,484 versus $26,255 for females. The per capita income for the county was $22,352. About 9.50% of families and 12.40% of the population were below the poverty line, including 18.10% of those under age 18 and 8.80% of those age 65 or over.