Harman Blennerhassett (1765 -1831), Irish-American lawyer, son of an Irish country gentleman of English stock settled in Co. Kerry, was born on October 8, 1765. He was educated at Trinity College, Dublin, and in 1790 was called to the Irish bar. After living for several years on the continent, he married in 1796 his niece, Margaret Agnew, daughter of Robert Agnew, the lieutenant-governor of the Isle of Man.
Ostracised by their families for this step the couple decided to settle in America, where Blennerhassett in 1798 bought an island in the Ohio river about 2 miles below Parkersburg, West Virginia. Here in 1805 he received a visit from Aaron Burr, in whose conspiracy he became interested, furnishing liberal funds for its support, and offering the use of his island as a rendezvous for the gathering of arms and supplies and the training of volunteers. When the conspiracy collapsed, the mansion and island were occupied and plundered by the Virginia militia. Blennerhassett fled, was twice arrested and remained a prisoner until after Burr's release.
The island was then abandoned, and Blennerhassett was in turn a cotton planter in Mississippi, and a lawyer (1819-1822) in Montreal, Canada. After returning to Ireland, he died in the island of Guernsey on February 2, 1831. His wife, who had considerable literary talent and who published The Deserted Isle (1822) and The Widow of the Rock and Other Poems (1824), returned to the United States in 1840, and died soon afterward in New York City while attempting to obtain through Congress payment for property destroyed on the island.