As of the census of 2000, there were 10,080 people, 4,235 households, and 2,511 families residing in the town. The population density was 3,583.7 people per square mile (1,385.0/km²). There were 4,444 housing units at an average density of 1,580.0/sq mi (610.6/km²). The racial makeup of the town was 92.82% White, 4.38% African American, 0.20% Native American, 1.41% Asian, 0.03% Pacific Islander, 0.27% from other races, and 0.90% from two or more races. Hispanic or Latino of any race were 1.22% of the population.
There were 4,235 households out of which 28.2% had children under the age of 18 living with them, 45.2% were married couples living together, 10.4% had a female householder with no husband present, and 40.7% were non-families. 35.2% of all households were made up of individuals and 14.8% had someone living alone who was 65 years of age or older. The average household size was 2.25 and the average family size was 2.94.
In the town the population was spread out with 22.1% under the age of 18, 8.2% from 18 to 24, 30.5% from 25 to 44, 21.8% from 45 to 64, and 17.4% who were 65 years of age or older. The median age was 39 years. For every 100 females there were 94.0 males. For every 100 females age 18 and over, there were 91.1 males.
The median income for a household in the town was $44,135, and the median income for a family was $58,299. Males had a median income of $42,412 versus $29,207 for females. The per capita income for the town was $23,737. 6.4% of the population and 4.0% of families were below the poverty line. Out of the total people living in poverty, 7.6% are under the age of 18 and 6.5% are 65 or older.
Bel Air is located on U.S. Route 1, and several miles north of I-95. Route 1 has both a bypass around Bel Air and Hickory, and a business route snaking through downtown. Both are connected by Maryland Route 24 to Interstate 95 in Edgewood.
In the early part of the 20th century the Maryland and Pennsylvania Railroad ("Ma and Pa") ran through town, but the tracks have since been dismantled. Much of the railroad's former route in and around Bel Air is now the Ma and Pa walking trail, which cuts through various wooded sections of town in and around Heavenly Waters Park. The main link runs from Williams Street downtown east to the Harford County Equestrian Center and on to Annie's Playground in Benson. A second link already built in Forest Hill was planned to merge with the main trail, but as of late 2006 the link has not been constructed.
A six-level parking garage is located on Hickory Avenue downtown, with plans to build a second parking garage elsewhere in town.