Harkness Memorial State Park is a historic preservation area with botanical garden and recreational features located on Long Island Sound in the town of Waterford, Connecticut.

The state park's 304 acres (123 ha) center around Eolia, a 42-room Renaissance Revival mansion with formal gardens and greenhouses.

[2] The park was the former summer home of philanthropists Edward and Mary Harkness, who inherited the fortune created by Edward's father, Stephen V. Harkness, who was a substantial investor in John D. Rockefeller's Standard Oil.

From 1918 to 1929, landscape designer Beatrix Jones Farrand made extensive improvements to the grounds, adding numerous formal gardens.

[3] The park offers mansion tours, picnicking, and shoreline fishing as well as private event rentals.