The U.S. Customshouse (now known as the Coast Guard Heritage Museum and the Donald G. Trayser Memorial Museum) is a historic customs house and United States Coast Guard museum on Cobbs Hill at 3353 Main Street (Massachusetts Route 6A) in Barnstable, Massachusetts. Built in 1855 to a design by Ammi Young, it was used as a custom house and post office until 1913, continuing to house the post office and other offices until 1958. It was converted into a museum in 1960, and was listed on the National Register of Historic Places in 1975.