Coplay is a borough in Lehigh County, Pennsylvania, six miles (10 km) northwest of Allentown. It is part of the Lehigh Valley region of the state. In 1900, 1,581 people lived in Coplay; in 1910, 2,670 people lived there. The population was 3,387 at the 2000 census. Coplay is included in the Allentown-Bethlehem-Easton, PA-NJ Metropolitan Statistical Area, which is also included in the New York City-Newark, New Jersey, NY-NJ-CT-PA Combined Statistical Area.
Coplay is located at 40°40′14″N 75°29′43″W (40.670521, -75.495395).
According to the United States Census Bureau, the borough has a total area of 0.6 square miles (1.6 km2), of which, 0.6 square miles (1.6 km2) of it is land and 0.04 square miles (0.10 km2) of it (3.08%) is water. The Borough of Coplay is situated along the Lehigh River, about 5 miles (8.0 km) north of Allentown.
Coplay was part of the 400 acres (1.6 km2) of land John Jacob Schreiber bought from the William Penn heirs in 1740. For a long time it was known as Schreibers. Later it was known as the Lehigh Valley, because of the Lehigh Valley Iron Furnaces that were located here.