[1] His parents were William Eustace of Castlemartin, the Lord Chancellor's younger brother, and Anne Netterville, daughter of Sir Robert Netterville of County Meath.
[2] Eventually the Chancellor made a will by which William inherited the great bulk of the property including the estate of Harristown, County Kildare, and the Eustace townhouse, Damask, on present-day Eustace Street in central Dublin.
[3] He sat in the Irish House of Commons as a Member of Parliament for Knocktopher between 1664 and 1666.
He married, firstly, Anne Colville, daughter of the prominent landowner and statesman Sir Robert Colville of Newtownards and his first wife Penelope Rawdon, and secondly Clotilda Parsons, daughter of Michael Parsons of Tomduff, County Wexford.
He had eight children but only three daughters survived him, Anne, Penelope and Clotilda, each of whom inherited a share of his estate.