The house was built about 1770 for Thomas Barclay, and was his house at the end of 1776, when George Washington occupied it as a military headquarters during the dark days of the New York and New Jersey campaign of the American Revolutionary War. After the war the house was purchased by Robert Morris, a signer of the Declaration of Independence, and the principal financier of the war effort. Morris fell upon financial hard times owing to failed real estate speculation, and sold the house in 1806 to George Clymer, another signer of the Declaration. It is Clymer who named the property "Summerseat", and it was his home until his death in 1813.