Until it was moved to the Leonis Adobe grounds in 1983, the Plummer House stood in Plummer Park in West Hollywood where it was known as "the oldest house in Hollywood." On January 11, 1935 the Plummer House was registered as State Historical Landmark No. 160.

Plummer Park was part of the Rancho La Brea originally granted to Antonio Jose Rocha and Nemisio Dominguez in 1828. The land which eventually became Plummer Park was acquired by the Plummer family in 1877. The Plummer ranch was bounded by present day Santa Monica Blvd., Gardner St., Sunset Blvd. and La Brea Ave. Sea Captain John Cornelius Plummer, his wife Maria Cecilia and their two sons John (Juan) and Eugene (Eugenio) soon built a house and barn and began growing vegetables to sell to Los Angeles residents.

Eugene Plummer, the Last of the Dons
The Plummer family and the Leonis family were acquaintances. In "Senor Plummer - The Life and Laughter of an Old Californian" Eugenio recounted how Espiritu Leonis would visit the Plummer family in Hollywood, where they played Spanish whist and reminisced about the old days. Espiritu's son Juan Menendez also wrote in his journal about visits between the families. After the deaths of Captain Plummer and Doņa Maria Plummer the land was gradually sold, until Eugenio was left with only about three acres. Los Angeles County acquired the property for a public park, and gave Eugenio permission to live there for the remainder of his life. Eugenio lived in his house at Plummer Park until he died on May 19, 1943 at the age of 91.

After Eugenio's death, the Plummer House was used by the Audubon Society to house their library and exhibits until 1980, when vandals set fire to the rear portion of the house. The City of Los Angeles was going to demolish the structure, but the Leonis Adobe Association made arrangements with Los Angeles County in 1983 to move the house to the Leonis Adobe property. The remaining portion of the Plummer House was restored and now serves as the visitor center and gift shop for the Leonis Adobe.

The Plummer house was restored to its original condition per correspondence with the State Historical Preservation Office. Pictures supplied by S.H.P.O. were used in the restoration. The horizontal shiplap siding was replaced where necessary with duplicates of the remaining material. The gingerbread on the eaves was restored to its original condition. The double hung windows are original. The tongue and groove fir flooring was replaced where necessary. The ceilings were restored with tongue and groove fir, matching the original remnants extant in 1983. The inner walls were restored in the same manner as the original, having bare wood covered with burlap and then wallpaper. The Association has built a rear wall, as the back half of the house was destroyed by fire. The roof shingles were replicas of the original; however, due to the new site being in a fire zone, the wood shingles were replaced with modern fire-resistant material. Missing interior doors were replaced with period doors found in salvage yards. Missing hinges were also replaced with those matching the extant hinges.