According to the 2000 Census, Mecklenburg County had a population of 695,454. There were about 174,986 families and 273,416 households in the county. The county's population density was 510/km², which is 1,322 people per square mile. At an average density of 556 per sq/ml, there were 292,780 housing units. Mecklenburg County is one of the most diverse counties in the country, with the 2000 census confirming this. 64.2% of the population was White, 27.87% African American or Black, 3.15% Asian, 0.34% Alaska Native/American Indian, and 3.01% from other races. People of Latino and Hispanic origin made up 6.45% of the population in the 2000 Census.
Out of the 273,416 households, 32.1% had children aged under 18 years living there. 47.7% of the households had married couples living together, and 12.4% belonged to single female householders with no husbands. 36.4% of the households were non-families. Individuals living alone made up 27.6% of all households, out of which 5.8% had people aged above 65 years. The average family size was 3.06, with the average household size at 2.49.
The 2000 census also showed that Mecklenburg County had a population with an evenly spread age count. 25.1% of the population were under 18 years, 9.7% aged 18-24, 36.4% aged 25-44, 20.3% aged 45-64, and 8.6% aged 65 years and older. The county's median age was 33 years. There were around 96.5 males for every 100 females. There were 93.6 males for every 100 females aged above 18 years.