The county is named for John Hardin, a Continental Army officer during the American Revolution. President Abraham Lincoln was born in what was then Hardin County near Hodgenville, now part of modern-day LaRue County.
As of the census of 2000, there were 94,174 people, 34,497 households, and 25,355 families residing in the county. The population density was 150 per square mile (58 /km). There were 37,673 housing units at an average density of 60 per square mile (23 /km). The racial makeup of the county was 81.99% White, 11.87% Black or African American, 0.42% Native American, 1.80% Asian, 0.22% Pacific Islander, 1.35% from other races, and 2.35% from two or more races. 3.35% of the population were Hispanics or Latinos of any race.
There were 34,497 households out of which 38.40% had children under the age of 18 living with them, 57.80% were married couples living together, 11.90% had a female householder with no husband present, and 26.50% were non-families. 22.80% of all households were made up of individuals and 7.50% had someone living alone who was 65 years of age or older. The average household size was 2.62 and the average family size was 3.07. The largest metropolitan area in the county is the City of Elizabethtown.
The age distribution was 27.60% under the age of 18, 10.60% from 18 to 24, 31.50% from 25 to 44, 20.60% from 45 to 64, and 9.70% who were 65 years of age or older. The median age was 34 years. For every 100 females there were 102.00 males. For every 100 females age 18 and over, there were 100.50 males.
The median income for a household in the county was $37,744, and the median income for a family was $43,610. Males had a median income of $30,743 versus $22,688 for females. The per capita income for the county was $17,487. About 8.20% of families and 10.00% of the population were below the poverty line, including 13.50% of those under age 18 and 8.60% of those age 65 or over.