Lehigh County is named after the Lehigh River (whose name is derived from the Delaware Indian term Lechauweki or Lechauwekink, meaning "where there are forks"), which runs through the county's two largest cities, Allentown and Bethlehem. It is located in the Lehigh Valley region of Pennsylvania, in the eastern part of the state.
As of the census of 2000, there were 312,090 people, 121,906 households, and 82,164 families residing in the county. The population density was 900 people per square mile (348/km²). There were 128,910 housing units at an average density of 372 per square mile (144/km²). The racial makeup of the county was 87.02% White, 3.56% Black or African American, 0.18% Native American, 2.10% Asian, 0.04% Pacific Islander, 5.28% from other races, and 1.83% from two or more races. 10.22% of the population were Hispanic or Latino of any race. 27.1% were of German, 7.9% Italian, 7.7% Irish, 6.2% Pennsylvania German and 5.6% American ancestry according to Census 2000. 85.0% spoke English, 8.4% Spanish and 1.2% Arabic as their first language.
There were 121,906 households out of which 30.60% had children under the age of 18 living with them, 53.00% were married couples living together, 10.50% had a female householder with no husband present, and 32.60% were non-families. 27.10% of all households were made up of individuals and 11.20% had someone living alone who was 65 years of age or older. The average household size was 2.48 and the average family size was 3.02.
In the county, the population was spread out with 23.90% under the age of 18, 8.10% from 18 to 24, 29.20% from 25 to 44, 23.00% from 45 to 64, and 15.80% who were 65 years of age or older. The median age was 38 years. For every 100 females there were 93.20 males. For every 100 females age 18 and over, there were 89.60 males.
Lehigh County's primary airport, Lehigh Valley International Airport (IATA: ABE, ICAO: KABE), is located three miles (5 km) northeast of Allentown in Hanover Township.
The county is also served by Allentown Queen City Municipal Airport, a two-runway general aviation facility located off of Allentown's Lehigh Street. Queen City is used predominantly by private aviation that was awarded General Aviation Airport of the year by the Eastern Region of the Federal Aviation Administration in 2006.
Public bus service in Lehigh County is available through the Lehigh and Northampton Transportation Authority, known as LANTA. Several private bus lines, including Bieber Tourways, Susquehanna Trailways and Trans-Bridge Lines, provide bus service from Allentown to New York City's Port Authority Bus Terminal, Philadelphia's Greyhound Terminal, Atlantic City's Bus Terminal, and other regional locations.