Lehigh, county, eastern Pennsylvania, U.S., consisting of a hilly region in the Appalachian Ridge and Valley physiographic province bordered by the Lehigh River to the east and Blue Mountain to the north. Other waterways include Leaser Lake and Jordan, Little Lehigh, and Saucon creeks. The Appalachian National Scenic Trail follows the Blue Mountain ridgeline.
During the American Revolution the Liberty Bell was sequestered in a church in Northampton (1777), which, when the county was formed in 1812, became the county seat and was later renamed Allentown (1838). The county’s name is derived from Lechauwekink (later shortened to Lecha), the Delaware Indian name for the Lehigh River, meaning “where there are forks.” With the advent of the Lehigh Canal (1829), the city developed as a centre for anthracite coal, iron, cement, and silk.
The counties of Lehigh and Northampton share the city of Bethlehem and other elements of the Lehigh Valley industrial complex. The principal boroughs are Emmaus, Catasauqua, Fountain Hill, and Slatington. The economy depends on services (health care and business), manufacturing (electronic equipment, food products, and textiles), and agriculture (fruit and field crops). Area 347 square miles (898 square km). Pop. (2000) 312,090; (2010) 349,497.