The Governor Duncan Mansion is a historic house located in Vandalia, Illinois. Built in 1853, it served as the residence of Governor Joseph Duncan, the state's first governor. The mansion showcases Greek Revival architecture and is notable for its elegant design and rich history. Today, the mansion is preserved as a museum, offering visitors a glimpse into 19th-century life. It features period furnishings and artifacts, providing educational tours that highlight the significance of the building and its former residents. The Governor Duncan Mansion is a key landmark in Illinois history and culture.