The Marconi Conference Center State Historic Park is a historic site and state park in Marshall, California. It is located in the Tomales Bay and features the property built and created by Guglielmo Marconi in the early 1900s.

Marconi was an Italian inventor, best known for being the father of long distance radio transmission and work on the radio telegraph system. He created the site now known as the Marconi Conference Center State Historic Park as a housing for his personnel who worked on his transpacific radio receiver station located nearby. It functioned as such until the station shut down in 1939. It then served as a unit of the Synanon from the 1960s to 1980s until it was acquired by a private foundation and given to the state.

The Marconi Conference Center State Historic Park is open by appointment only.