William Wagner House, Wooden frame house in Miami, United States.

The William Wagner House is a vernacular wood-frame house in Lummus Park, on the north bank of the Miami River at NW 4th Avenue and NW 3rd Street. It is built with balloon frame construction, in which closely spaced studs run the full height of the walls. It is the oldest known house still standing in Miami.

William Wagner, a U.S. Army veteran wounded at the Battle of Cerro Gordo in the Mexican War, built the house c. 1855 after his former unit was sent to reopen Fort Dallas. He lived there until his death in 1901. In 1979 the Dade Heritage Trust moved it from its original site near Culmer Metrorail Station to Lummus Park.

The house reflects early Miami settlement patterns, built by William Wagner who arrived with his Creole wife Everline. It tells the story of the first families who established themselves in the area and how they shaped their living spaces.

The house stands in Lummus Park on the north bank of the Miami River, at the corner of NW 4th Avenue and NW 3rd Street in downtown Miami. It is a street-level structure in an open public park, reachable on foot from the surrounding downtown blocks and by Metrorail, whose Culmer station sits near the home's original riverside site.

The house is the only known surviving 19th-century house in Miami, and it is also noted for its use of balloon frame construction, a rare example of vernacular wood frame architecture. It was moved in 1979 by the Dade Heritage Trust from its original site near Culmer Metrorail Station to Lummus Park.