Blennerhassett Island Historical State Park is a state park located on Blennerhassett Island, a small island in the Ohio River, located in Wood County, West Virginia, USA. The property was the site of a Palladian mansion owned by Harman Blennerhassett, a participant in some of the alleged intrigues of Aaron Burr, and his wife Margaret Agnew. While the original mansion burned to the ground in 1811, a detailed replica, which can be toured, was built on its foundations in the 1980s. The Blennerhasset mansion greatly resembled George Washington's Mount Vernon, due to its Palladian style.

Harman Blennerhassett was an Anglo-Irish lawyer, a member of the Society of United Irishmen who emigrated in advance of their rebellion in 1798 to become a socially and politically distinguished plantation owner in then-western Virginia. Implicated in the Burr conspiracy, an alleged military plot with Britain to separate the Louisiana Territory from the American Union, he was twice arrested and financially ruined. His last years were spent in England.