Thaddeus Kosciuszko National Memorial, at 301 Pine Street in Philadelphia, Pennsylvania, preserves the home of Tadeusz (Thaddeus) Kościuszko. Instructed to find "a dwelling as small, as remote, and as cheap" as possible, Kosciuszko's secretary, Julian Ursyn Niemcewicz, chose Mrs. Ann Relf's boarding house in Society Hill (on the corner of 3rd and Pine Streets). The life and work of the Polish patriot and hero of the American Revolution are commemorated here.
The home was listed on the National Register of Historic Places on December 18, 1970. The National Memorial was authorized on October 21, 1972. It is administered under Independence National Historical Park, but is counted as a separate unit of the national park system.
At 0.02 acre (80 m²), the memorial is often referred to as America's smallest national park (or unit of the National Park System). Benjamin Franklin National Memorial is even smaller (only a statue), but that national memorial is designated an affiliated area rather than a unit because it is not administered by the federal government.