city, seat (1812) of Lehigh county, eastern Pennsylvania, U.S. Situated on the Lehigh River, Allentown, with Bethlehem and Easton, forms an industrial complex. William Allen, mayor of Philadelphia and later chief justice of Pennsylvania, laid out the town (1762), naming it Northampton. It was incorporated as the borough of Northampton in 1811 and was later (1838) officially renamed Allentown for its founder.

Construction of a bridge (1812) across the Lehigh and opening of the Lehigh Canal (1829) brought new economic opportunities to the town; an iron industry was started in 1847, a cement plant in 1850, and a rolling mill in 1860. Allentown's location amid rich mineral deposits (iron ore, zinc, limestone) and fertile farmland enhanced its development as an industrial and market centre. Manufacturers in the Allentown area produce natural gas and chemical products, electronics, trucks, and medical supplies.

The Allentown area is the seat of four colleges—Muhlenberg (1848), Cedar Crest (1867), Allentown College of St. Francis de Sales (1964), Lehigh Carbon Community College (1966)—and the Lehigh Valley campus (formerly Allentown campus; 1912) of Berks-Lehigh Valley College of Pennsylvania State University (Penn State Lehigh Valley). The Liberty Bell Shrine contains a full-size replica of the original bell, which was brought to Allentown during the American Revolution for safekeeping in the Zion Reformed Church. Herds of bison, deer, and elk roam the Trexler-Lehigh County Game Preserve. Inc. city, 1867. Pop. (1990) city, 105,090; Allentown-Bethlehem-Easton MSA, 595,081; (2000) city, 106,632; Allentown-Bethlehem-Easton MSA, 637,958.