Vegetation classification and mapping of U.S. National Vegetation Classification associations were conducted at the Sagamore Hill National Historic Site, creating current digital geospatial databases for the park. This study of the Sagamore Hill National Historic Site identified and characterized 10 U.S. National Vegetation Classification associations in detail. The diversity and distribution of vegetation associations is primarily a result of the following four factors: 1) the geologic history of the region, especially the effect of glaciation; 2) the park's position on the northeastern U.S. coastal plain within a temperate climate; 3) proximity to Long Island Sound and maritime ecological processes, such as diurnal tides, storm overwash, salt spray, and high winds; and 4) the park's setting within a suburban landscape with a moderately intensive human land use history, along with its associated problems, such as invasive species, fragmentation, habitat loss, and pollution.