Mill Ends Park lies in the median strip along Naito Parkway in downtown Portland, Oregon, holding the Guinness Book of World Records for being the smallest park in the world, consisting of a small cement circle spanning a whopping two feet across.  Seems like the park is in need of a little care as it appears to be 90% overgrown by plants.  Mill Ends Park was officially dedicated on St. Patrick's Day in 1948.  According to a nearby sign:

From his office on the second floor of the old Oregon Journal building, journalist Dick Fagen (1911-1969) periodically gazed down on the busy Front Avenue thoroughfare.  It was his keen imagination that turned a utility pole hole, in the avenue's median strip at Taylor Street, into "Mill Ends Park".  The Guinness Book of World Records lists it as the world's smallest park.  It is twenty-four inches in diameter, & contains 452.16 square inches of land.  In his "Mill Ends" column in the Oregon Journal, Fagan described a variety of events occurring in the park, which were presided over by Patrick O'Toole, head Leprechaun residing in the park.  Weddings and other celebrations have taken place at Mill Ends, & on St. Patrick's Day, 1976, the site was dedicated as an official park of the City of Portland.