During the Industrial Revolution, the Lehigh River served a vital role in the nation's development by offering one of the first transportation and trading routes for mining products, including anthracite, iron, manganese, limestone, and ultimately manufactured steel products.

"[7] Shelter House, constructed in Emmaus in 1734 by Pennsylvania German settlers, is the oldest continuously occupied structure in both Lehigh County and Lehigh Valley and among the oldest still-standing building structures in the U.S. state of Pennsylvania.

[5][6] Some of the first resistance to British colonialism, which led ultimately to the American Revolutionary War, began in present-day Lehigh County.

After Washington and the Continental Army were defeated at the Battle of Brandywine on September 11, 1777, the revolutionary capital of Philadelphia was left defenseless and Pennsylvania's Supreme Executive Council ordered that eleven Philadelphia bells, including the Liberty Bell (then known as the State House Bell), be taken down and moved to present day Allentown (then called Northampton Towne) and hidden in the basement of Zion Reformed Church on present day West Hamilton Street to protect them from being melted down by the British Army for use as munitions.

The opening of the Lehigh Canal beginning in 1827 transformed Allentown and Lehigh County from a rural agricultural area dominated by German-speaking people into an urbanized industrialized area and expanded the city's commercial and industrial capacity greatly.

Following the Union Army's defeat at the Battle of Fort Sumter and Lincoln's April 15, 1861, proclamation calling for state militia to provide 75,000 volunteer troops to defend the nation's capital of Washington, D.C., Allentown deployed the Allen Infantry, also known as the Allen Guards and composed of volunteers from Allentown and its surrounding suburbs.

As the Civil War progressed, multiple Union Army units were drawn from Lehigh County, including roughly seventy percent of the 47th Pennsylvania Infantry Regiment.

On October 19, 1899, a monument in honor of the Lehigh County men killed in their volunteer service to preservation of the Union, the Soldiers and Sailors Monument, was erected at Seventh and Hamilton streets in Center City Allentown, where it still stands.

The Lehigh County's highest point is near Germansville at Bake Oven Knob, a mass of Tuscarora conglomeratic rocks that rise about 100 feet (30 m) above the main Blue Mountain ridge in northwestern Heidelberg Township.

The variety is hot-summer (Dfa) except in the county's higher elevation areas, where it is warm-summer (Dfb).

Summers are typically hot and muggy, fall and spring are generally mild, and winter is cold.

Rainfall is generally spread throughout the year with eight to twelve wet days per month,[13] at an average annual rate of 110.54 centimetres (43.52 in).

[27] School districts include:[30] Lehigh County's primary commercial airport is Lehigh Valley International Airport (IATA: ABE, ICAO: KABE), located in Hanover Township in the county.

The Morning Call (in Allentown), The Express-Times (in Easton), and The Times News (in Lehighton) each cover Lehigh County.

Numerous New York City radio and television stations are also carried in the county.

Lehigh County also has 25 acres (100,000 m2) of public parks, including: Under Pennsylvania law, there are four types of incorporated municipalities: cities, boroughs, townships, and, in only one case, towns.

The following cities, boroughs, and townships are located in Lehigh County: Census-designated places are geographical areas designated by the U.S. Census Bureau for the purposes of compiling demographic data.