[2] The family is recorded as having originally been settled in Cumberland in northern England, at the manor of Blennerhasset.
In 1547 the Blennerhassett family relocated to Frenze, Norfolk and Barsham, Suffolk on former monastery lands.
In the reign of Elizabeth I the senior branch of the family under Robert Blennerhassett (accompanied by his elderly father Thomas) settled in County Kerry, Ireland, during the Plantation of Munster,.
[7] Many members of the family married into other Kerry dynasties such as the Conways, Dennys, Crosbies, Fitzmaurices, O'Connells, Sealys, Springs and Mullins.
In 1809, Rowland Blennerhassett, a lawyer and politician, was created a baronet in the Baronetage of the United Kingdom.