As of the census of 2000, there were 14,972 people, 6,684 households, and 3,689 families residing in the city. The population density was 2,977.4 people per square mile (1,149.2/km²). There were 7,432 housing units at an average density of 1,478.0/sq mi (570.5/km²). The racial makeup of the city was 83.90% White, 11.63% African American, 0.40% Native American, 0.63% Asian, 0.02% Pacific Islander, 1.26% from other races, and 2.17% from two or more races. Hispanic or Latino of any race were 2.91% of the population.
In the city the population was spread out with 23.1% under the age of 18, 9.6% from 18 to 24, 28.7% from 25 to 44, 22.3% from 45 to 64, and 16.4% who were 65 years of age or older. The median age was 37 years. For every 100 females there were 91.0 males. For every 100 females age 18 and over, there were 88.6 males.
The median income for a household in the city was $29,495, and the median income for a family was $36,954. Males had a median income of $29,697 versus $22,212 for females. The per capita income for the city was $16,314. About 14.7% of families and 20.0% of the population were below the poverty line, including 28.8% of those under age 18 and 15.1% of those age 65 or over.
Amtrak provides service to Martinsburg. The city's passenger rail station is located downtown at 229 East Martin Street. MARC, Maryland's commuter rail system, operates trains on weekdays on its Brunswick Line which terminates in Martinsburg. Service is provided to Union Station in Washington, D.C.
Eastern Panhandle Transit Authority, known more popularly as "Pan Tran," operates bus routes in Martinsburg, surrounding Berkeley County, and neighboring Jefferson County, West Virginia.
Eastern WV Regional Airport, south of the city, handles general aviation. The closest airport with commercial air service is Hagerstown Regional Airport, that is about 25 miles driving distance north. The closest international airport is Washington Dulles International Airport, which is about 60 miles driving distance east.