The Blennerhassett family is an English and Anglo-Irish noble family which has been involved in the politics of Britain and Ireland since the fourteenth century.  A powerfully well connected family, members have been involved in all aspects of society. The vast majority of the research below is taken from existing study of the family and from such books as, Selections From Old Kerry Records, or from research notes, Estated Gentlemen of Kerry, principally from the Revolutionary and Napoleonic Eras, their Births, Marriages, and Obituaries, from the Contemporary Press. Through my own research, I have added more information on branches. Below is a summary of some of the family members. 

Research begins with Thomas Blennerhassett born before 1500 and died after 1522, of Carlisle, Cumberland, England, whose son, John Blennerhassett (B. Abt. 1517 D.1578), of Carlisle, Cumberland, England, married Janet de Martindale, born 1534.  Their son, Thomas Blennerhassett (B. Abt. 1547 D.1611), born Flimby, Cumbria, England, married Mary Heydon (B.1642) in 1654. Thomas and Mary had the following children: 

Thomas (1565-1654), John (1560 - 1677), Robert (1565 - 1654), Blennerhassett (B.1568), Thomas (1577 - 1590), Thomas (1590 - 1590), and William (D.1621)

Of the above children, it was John and Robert, who moved from Cumbria, England to Ireland. The following lineage will follow Robert Blennerhassett, born Flimby, Cumbria England and moved to Kerry, Ireland. He was MP for Tralee and was occupying Ballysheedy and Ballycarty Castles. Robert married Elizabeth Conway, daughter of Jenkin Conway & Mary Herbert, of Castle Conway. Elizabeth was the sister of Jenkin (m. Avice Dalton) and Alice Conway (m. Edward Roe). Robert and Elizabeth had the following children: 

1 John Blennerhassett (1593 - 1676) born Castle Conway, he married Martha Lynne and had the following children: 

i John Blennerhassett, (D. 1677) married Elizabeth Denny, daughter of Sir Edward Denny, Knight with children: 

John Blennerhassett (D.1709), was M.P for Tralee, Dingle and Co. Kerry. John married Margaret Crosbie (1670 - 1759 - Ref: Irish Historic Houses) of Tubrid House, Kerry, which was built by the Crosbie family. Following John's death in 1709, Margaret married David John Barry, son of Richard Barry, 2nd Earl of Barrymore with no further children. John Blennerhassett and Margaret Crosbie had several children with one of their sons being, Colonel John Blennerhassett (1691-1775) who made a family pact Maurice Crosbie of Ardfert and Arthur Denny of Tralee, partitioning the county representation among the three families (Ref: Irish Historic Houses). Colonel John's son, John Blennerhassett (1715 - 1763) married Anne Crosbie, daughter of William Crosbie of Tubrid, County Kerry. Another son of John and Margaret, was William Blennerhassett (1705 - 1785), married Mary, daughter of John Morley, Mayor of Cork. 

ii Robert Blennerhassett, (Captain and M.P.) married Avice Conway, (D. 1663) his 2nd cousin. Avice is the daughter of Edward Conway and grand daughter and co-heiress of Jenkin Conway. Robert and Avice had twelve children, with some of them as follows:  

John Blennerhassett (D.1738), inherited Castle Conway. 

Henry Blennerhassett (1693 - 1728), who married Dorcus (Alice) Crumpe, daughter of Thomas Crumpe (of Meath) and Dorcas Orpen (2nd dau of Robert Orpen, who married Lucy Chichester, brother to Richard Orpen, of the Whitehouse). Dorcas Crumpe was the brother to Samuel Crumpe, who married Lucy Loughlin, daughter of Brester Loughlin of Mount Loughlin. 

Henry and Dorcus had eleven children (7 sons & 4 daughters), with one of their daughters, Lucy Blennerhassett, born 1713 of Castle Conway, who married, her 3rd cousin, John Heaphy, son of Daniel Heaphy & Rachel Blennerhassett, who had the following known children:

John Heaphy (father of Lucinda Heaphy, who married Hamilton White, brother to Lord Bantry), (See Heaphy of Limerick & Kerry). 

Catherine Blennerhassett, was an other daughter, who married firstly to Richard McLoughlin, and had two daughters, Elizabeth (married Lieutenant Miles Martin, of Co. Down, before 1708) and Avis McLoughlin ((D.1750, Killarney), married John Mason, g grandson of Sir John Mason of Sion House, London, before 1705, with children: Catherine (m. Francis Spring), James, Barbara, Richard, John  and Ellen). Catherine marries secondly to John Conway before 1695 (Ref: Court of Exchequer), a descendent of Jenkin Conway, and had one known daughter, named Mildred Conway, who married Thomas Jeffcott of Tralee, whose daughter, Catherine Jeffcott, married Moses LaPlant (D.1785), a surgeon from Cork in 1741. 

iii Thomas Blennerhassett, married Ellen Stoughton, daughter of Anthony Stoughton and Honora O'Brien, daughter of the 5th Baron of Inchiquin, Co. Clare and 12th in Royal Descent from King Edward III. Thomas and Ellen had seven children. 

iv Mary Blennerhassett, married Mr. Fitzmorris. 

v Alice Blennerhassett, married Edward Conway, of Castle Conway, her cousin, son of Captain James Conway (Of Dublin, unknown if related to the Kerry Conways) and Elizabeth Roe. One son, James Conway of Cloghane, who married Catherine Fitzgerald, daughter of Patrick Fitzgerald, son of the Knight of Kerry. 

vi Lucy Blennerhassett, married John Walker, lieutenant in the British Army in 1641. 

vii Elizabeth Blennerhassett 

2 Edward Blennerhassett, (1595 - 1666), of Ballycarty Castle, he was High Sheriff of Kerry in 1642. Edward married Mary Vauclier, a descendent of Lord Vauclier of France, Governor Calais in 1470. Edward and Mary had one daughter, named Anne Blennerhassett, who married Captain John Baker of Castle Eve in Co. Kilkenny. 

3 Arthur Blennerhassett, (1625 - 1695) 3rd son, of Ballycarty Castle, Kerry, and later of Loughgur and Herberstown, Co. Limerick. Captain. Arthur married Mary Fitzgerald, of Ballynard, Limerick (dau. of Ven. Gerald Fitzgerald, Archdeacon of Emly) and they had the following children: 

i Edward Blennerhassett, (D.1728), of Limerick, and took ownership of Riddlestown House through the marriage with Elizabeth Windall, who inherited the house from her mother, with their son, Rice Blennerhassett, of Riddlestown House, Rathkeale, Limerick. 

ii Robert Blennerhassett, (1652 - 1712), born Loughgur, Limerick and later Burgess of Clonmel and MP. Robert married Alice Osborne, daughter of Sir Thomas Osborne, of Waterford and widow of Thomas Warter of Cullen, Limerick. Their son was the Honourable Justice Arthur Blennerhassett (1687 - 1758), judge, who married firstly to Mary Pope and secondly to Mary Rice and daughters: Mary Blennerhassett (M. Thomas Squire), Elizabeth Blennerhassett (M. Eugene O'Lavery in 1729), Annabella Blennerhassett (M. John Grove in 1710, Cork) and Alice Blennerhassett. 

iii John Blennerhassett, (1660 - 1677)

iv Thomas Blennerhassett, (D.1709), of Kerry, and deputy Seneschal for Trinity College Dublin's Munster Estates. Thomas married Ruth Blennerhassett, his cousin, daughter to Thomas Blennerhassett and Elizabeth Denny of Ballysheedy, Kerry. Ruth was originally married to Captain Thomas Browne, of Cork. They had two daughters: Mary and Jane (married Richard Hall) Blennerhassett. 

v Arthur Blennerhassett, (1664 - 1696), he was a medical doctor, educated at Trinity College 

vi Gerald Blennerhassett, (1672 - 1758), 6th son, of Kerry and Riddlestown, Co. Limerick. Gerald married Christina Baley (Bailey), of Loughgur, sister to Henry Baley, who married Gerald's sister, Ellen Blennerhassett. Arthur and Christina had the following children: 

Arthur Blennerhassett, of Riddlestown Park, magistrate, he married Margaret (Celinda) Hayes. Arthur and Margaret had two sons, Hayes and Gerrard, and one daughter, Ellen. 

Mary Blennerhassett, eldest daughter, married Maurice Wall, barrister of Dunmoylan, Co. Limerick. Mary and Maurice had one son named John, who died young and a daughter, Mary, who died unmarried. 

Rachel Blennerhassett, (1696 - Aft 1763), 2nd daughter married Daniel Heaphy (1689 - Aft 1763 - related to the Tottenham/Atkin families of Wexford), of Co. Limerick. Rachel & Daniel had the following known children up to 1733: 

John (married Lucy Blennerhassett, his cousin, of Castle Conway), Gerrard, Blennerhassett, Robert, Tottenham, Arthur, Mary, Annabella, & Christina Heaphy. (See Heaphy of Limerick & Kerry)

Anabella Blennerhassett, 3rd daughter. Did not marry. 

Eleanor Blennerhassett, 4th daughter, married Thomas Spiers Gabbot, of Co. Limerick. They had one daughter, Ellen Spiers Gabbot. 

Elizabeth Blennerhassett, 5th daughter, married William Harding, of Co. Limerick. 

Christina Blennerhassett, 6th daughter, married Thomas Lloyd, of Kildroman, Limerick.  

vii William Blennerhassett, (1671 - 1691)

viii Elizabeth Blennerhassett, (1669 - 1677)

ix Annabella Blennerhassett, (1670 - 1695), married Captain Abraham Green of Ballymacreece, Limerick (See Green Family ). 

x Ellen Blennerhassett, (D. Bef. 1695), she married Henry Bayley, sister to Christina, who married Ellen's brother, Gerald. Henry and Christina Bayley, are the children of Henry & Susannah Bayley, and siblings to Tyrell Bayley and Sexton Bayley, cousin to Edmond Sexton Pery. 

4 Elizabeth Blennerhassett, b.1600, of Ballycarty Castle, she married George Norton, Captain of Moyagh Castle, Co. Clare. Their daughter, Elizabeth Norton, married Agustine Fitzgerald, and their son, William Fitzgerald, married Jane Bryan of Kilkenny, with their daughter, Ellen Fitzgerald, marrying Henry Ivers of Mount Ivers Court, Sixmilebridge, Co. Clare. 

Disconnected Family: 

James Blennerhassett of Garfinny, Dingle, possibly born about 1680?  COI records have him married to Sarah and they had the following children: 

i Thomas Blennerhassett B. 1707, who married Mary with children: 

Sarah, Robert, Ann, James, F.R, & Margaret Jane Blennerhassett.  

ii Mary Blennerhassett B.1710

iii Martha Blennerhassett B.1713 D.1722

iv Margaret Blennerhassett B.1715 D. 1740

v Elizabeth Blennerhassett B.1716

vi Jane Blennerhassett B.1717

vii John Blennerhassett B.1719 D.1722

viii James Blennerhassett B.1721 D.1722

ix William Thomas Blennerhassett B.1722 D.1725

James and Sarah may have had the following 3 children born before 1707:

i Ann Blennerhassett B. abt 1701, who married Frederick Browne in 1721 of Ventry with a daughter Triphena Browne, who married Alexander Eager in 1742 

ii Sarah Blennerhassett B. abt 1702, who married James Fitzgerald in 1723 of Ventry with a daughter, Sarah Fitzgerald, born 1740

iii Arthur Blennerhassett, who married Sarah, with two children, Joseph and Sarah Blennerhassett.