As an unincorporated area, Darnestown's boundaries are not officially defined. Darnestown is, however, recognized by the United States Census Bureau as a Census-designated Place, and by the United States Geological Survey as a populated place located at 39°6'5" North, 77°16'52" West (39.101429, -77.281236)1.
According to the United States Census Bureau, the place has a total area of 45.8 km² (17.7 mi²). 42.9 km² (16.6 mi²) of it is land and 2.9 km² (1.1 mi²) of it is water. The total area is 6.27% water.
As of the census of 2000, there are 6,378 people, 2,038 households, and 1,830 families residing in the area. The population density is 148.5/km² (384.6/mi²). There are 2,064 housing units at an average density of 48.1/km² (124.5/mi²). The racial makeup of the area is 85.06% White, 3.95% African American, 0.25% Native American, 7.92% Asian, 0.03% Pacific Islander, 0.58% from other races, and 2.21% from two or more races. 3.23% of the population are Hispanic or Latino of any race.
There are 2,038 households out of which 47.9% have children under the age of 18 living with them, 83.3% are married couples living together, 4.1% have a female householder with no husband present, and 10.2% are non-families. 7.5% of all households are made up of individuals and 2.3% have someone living alone who is 65 years of age or older. The average household size is 3.13 and the average family size is 3.29.
In the area, the population is spread out with 30.7% under the age of 18, 4.5% from 18 to 24, 25.5% from 25 to 44, 31.8% from 45 to 64, and 7.5% who are 65 years of age or older. The median age is 40 years. For every 100 females there are 98.8 males. For every 100 females age 18 and over, there are 96.0 males.
The median income for a household in the area is $130,626, and the median income for a family is $136,507. Males have a median income of $90,476 versus $56,958 for females. The per capita income for the area is $52,466. 2.2% of the population and 1.5% of families are below the poverty line. Out of the total people living in poverty, 1.0% are under the age of 18 and 5.2% are 65 or older.