The name Oconee is generally believed to be derived from a Hitichi (Creek) word meaning "land of springs". When the county was first formed, the name was picked up from the Yuchi Tribe (Creek) which was prevalent around Anderson and Pendleton, the seat of the district government. An alternative theory holds that the name and meaning came from the Cherokee language.
As of the census of 2000, there were 66,215 people, 27,283 households, and 19,589 families residing in the county. The population density was 106 people per square mile (41/km²). There were 32,383 housing units at an average density of 52 per square mile (20/km²). The racial makeup of the county was 89.14% White, 8.38% Black or African American, 0.22% Native American, 0.35% Asian, 0.02% Pacific Islander, 1.06% from other races, and 0.82% from two or more races. 2.36% of the population were Hispanic or Latino of any race. 26.5% were of American, 13.1% Irish, 11.9% German and 10.5% English ancestry according to Census 2000.
There were 27,283 households out of which 28.50% had children under the age of 18 living with them, 57.80% were married couples living together, 10.10% had a female householder with no husband present, and 28.20% were non-families. 24.70% of all households were made up of individuals and 9.50% had someone living alone who was 65 years of age or older. The average household size was 2.40 and the average family size was 2.85.
In the county, the population was spread out with 22.90% under the age of 18, 8.00% from 18 to 24, 27.40% from 25 to 44, 26.20% from 45 to 64, and 15.60% who were 65 years of age or older. The median age was 40 years. For every 100 females there were 96.70 males. For every 100 females age 18 and over, there were 93.50 males.
The median income for a household in the county was $36,666, and the median income for a family was $43,047. Males had a median income of $31,032 versus $22,156 for females. The per capita income for the county was $18,965. About 7.60% of families and 10.80% of the population were below the poverty line, including 14.00% of those under age 18 and 12.90% of those age 65 or over.