Mill Ends Park

Mill Ends Park is an extremely small urban park, consisting of one tree, located in the median strip of SW Naito Parkway next to Tom McCall Waterfront Park along the Willamette River near SW Taylor Street in the downtown core of Portland, Oregon, United States. The park is a small circle 2 ft across, with a total area of 452 sq in. It is the smallest park in the world, according to the Guinness Book of Records, which first granted it this recognition in 1971, though this title may be soon given to a 2022 park in Talent, Oregon, which is 78 sq in smaller.

Source: Wikipedia