As an unincorporated area, Olney's boundaries are not officially defined. The United States Census Bureau defines a Census-Designated Place of Olney centered at 39°9' North 77°5' West. The United States Geological Survey considers Olney as a place whose center is at latitude 39°9'11" North, longitude 77°4'2" West. Other organizations may use their own definitions. As of the 2000 census, the area had a total population of 31,438.
As of the census of 2000, there are 31,438 people, 10,274 households, and 8,650 families residing in the area. The population density is 934.4/km² (2,420.1/mi²). There are 10,415 housing units at an average density of 309.6/km² (801.7/mi²). The racial makeup of the area is 79.04% White, 8.78% African American, 0.25% Native American, 8.03% Asian, 0.04% Pacific Islander, 1.64% from other races, and 2.21% from two or more races. 5.01% of the population are Hispanic or Latino of any race.
There are 10,274 households out of which 49.1% have children under the age of 18 living with them, 71.4% are married couples living together, 10.2% have a female householder with no husband present, and 15.8% are non-families. 12.3% of all households are made up of individuals and 2.7% have someone living alone who is 65 years of age or older. The average household size is 3.04 and the average family size is 3.34.
In the area, the population is spread out with 31.2% under the age of 18, 5.6% from 18 to 24, 29.9% from 25 to 44, 26.9% from 45 to 64, and 6.4% who are 65 years of age or older. The median age is 37 years. For every 100 females there are 93.5 males. For every 100 females age 18 and over, there are 89.0 males.
The median income for a household in the area is $94,818, and the median income for a family is $100,717. Males have a median income of $69,911 versus $45,818 for females. The per capita income for the area is $35,267. 2.6% of the population and 1.9% of families are below the poverty line. Out of the total people living in poverty, 3.4% are under the age of 18 and 3.0% are 65 or older.