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 located at 40°40′14″N 75°29′43″W / 40.67056°N 75.49528°W / 40.67056; -75.49528 (40.670521, -75.495395).
According to the United States Census Bureau, the borough has a total area of 0.6 square miles (1.7 km²), of which, 0.6 square miles (1.6 km²) of it is land and 0.04 square miles (0.1 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.