Cornwall is a borough in Lebanon County, Pennsylvania, United States. It is part of the Lebanon, PA Metropolitan Statistical Area. The population was 3,486 at the 2000 census.
Cornwall was founded by Peter Grubb in 1737. Peter, a Chester County stonemason, came to Lancaster County around 1734 in search of building materials. First building his house and then a store, he discovered very high quality magnetite iron ore nearby and decided to mine for it, acquiring 300 acres (1.2 km2) by 1737 and over 1,000 acres (4.0 km2) by 1739 when mining was initiated. He called it the Cornwall Iron Mines after his father's birthplace in Cornwall, England. The Cornwall Iron Mines, also known as Cornwall Banks, turned out to be the largest United States' iron deposit east of Lake Superior, and were once the largest open-pit iron mine in the world. They were mined continuously until 1973, totaling 234 uninterrupted years of production.
Finding the necessary components nearby for making iron (water, limestone and timber for charcoal), Grubb built the Cornwall Iron Furnace and began production in 1742. The operation also included the Hopewell Forges on nearby Hammer Creek. Peter Grubb did not stay long to run the operation, but leased it out in 1745 for 20 years and returned to Wilmington, Delaware. In 1765 Peter's sons Curtis and Peter Jr. took over the operation, and in 1798 it passed to Robert Coleman and his family. Cornwall Furnace was in production from 1742 until 1883, and appears today much as it was when production ended. In 1932 the Coleman family deeded the property to the Commonwealth of Pennsylvania and it is now a designated National Historic Landmark open to the public.