According to the U.S. Census Bureau, the county has a total area of 199 square miles, of which, 197 square miles is land and 2 square miles is water.

Adjacent Counties

• Fulton County (north)
• Clayton County (east)
• Spalding County (south)
• Coweta County (west)

As of the census of 2000, there were 91,263 people, 31,524 households, and 25,975 families residing in the county.  The population density was 463 people per square mile.  There were 32,726 housing units at an average density of 166 per square mile.  The racial makeup of the county was 83.87% White, 11.47% Black or African American, 0.21% Native American, 2.42% Asian, 0.02% Pacific Islander, 0.76% from other races, and 1.25% from two or more races.  2.83% of the population were Hispanic or Latino of any race.

There were 31,524 households out of which 43.10% had children under the age of 18 living with them, 71.50% were married couples living together, 8.30% had a female householder with no husband present, and 17.60% were non-families.  15.00% of all households were made up of individuals and 5.50% had someone living alone who was 65 years of age or older.  The average household size was 2.88 and the average family size was 3.20.

In the county the population was spread out with 29.10% under the age of 18, 6.50% from 18 to 24, 27.70% from 25 to 44, 27.80% from 45 to 64, and 8.90% who were 65 years of age or older.  The median age was 38 years.  For every 100 females there were 95.80 males.  For every 100 females age 18 and over, there were 92.00 males.

The median income for a household in the county was $71,227, and the median income for a family was $78,853.  Males had a median income of $54,738 versus $33,333 for females.  The per capita income for the county was $29,464.  About 2.00% of families and 2.60% of the population were below the poverty line, including 2.80% of those under age 18 and 4.60% of those age 65 or over.