Bethlehem is a city along the Lehigh River in Northampton and Lehigh counties in the Lehigh Valley region of the eastern portion of the U.S. state of Pennsylvania. As of the 2010 census, the city had a total population of 74,982, making it the seventh largest city in Pennsylvania, after Philadelphia, Pittsburgh, Allentown, Erie, Reading, and Scranton. Of this, 55,639 were in Northampton County, and 19,343 were in Lehigh County.
Bethlehem lies in the center of the Lehigh Valley, a region of 731 sq mi (1,890 km2) that is home to more than 800,000 people. Together with Allentown and Easton, the Valley embraces the Allentown-Bethlehem-Easton, PA-NJ metropolitan area, including Lehigh, Northampton, and Carbon counties within Pennsylvania, and Warren County in the adjacent state of New Jersey. Smaller than Allentown but larger than Easton, Bethlehem is the Lehigh Valley's second-most populous city. In turn, this metropolitan area comprises Pennsylvania's third-largest metropolitan area.
There are four general sections of the city: central Bethlehem, the south side, the east side, and the west side. Each of these sections blossomed at different times in the city's development and each contains areas recognized under the National Register of Historic Places. ZIP codes that use the address Bethlehem totaled 116,000 in population in the year 2000. These ZIP codes include Bethlehem Township and Hanover Township.
The Norfolk Southern Railway's Lehigh Line (formerly the main line of the Lehigh Valley Railroad), runs through Bethlehem heading east to Easton, Pennsylvania and Phillipsburg, New Jersey across the Delaware River. The Norfolk Southern Railway's Reading Line runs through Bethlehem heading west to Allentown and Reading.