Cassiobury was part of the lands owned by the Abbot of St Albans in Casho Hundred until The Dissolution the Monastries where the Abbey's lands were taken into crown ownership during the reign of Henry VIII. Cassiobury was granted (or sold) to the Lord of the Manor Sir Richard Morrison.
It became part of the property of (Arthur 1st Baron Hadham) on his marriage to the heiress, Elizabeth Morrison (Great Grandaughter of Sir Richard Morrison).
Arthur Capel 2nd Baron Hadham, who had inherited it from his father's was created Viscount Munden and Earl of Essex in 1661
Little Cassiobury a dower house, for whom ?
Was it commissioned to be built for the 1st Earl's mother (formerly Elizabeth Morrison , the heiress of Cassiobury), or his wife (formerly Elizabeth Percy, daughter of the Earl of Northumberland).
The first (died in 1660). Her husband, Arthur Capel, 1st Baron Hadham, was executed by the Comonwealth during the Civil War (March 1649), and his property was sequestrated. His widow Lady Elizabeth Capel (nee Morrison) successfully petitioned Parliament for it to be returned to her as it was rightfully her inheritance (7-8th May 1649).
Her daughter in-law (died in 1718). Her husband, the Earl of Essex, served Charles II as the ambassador to Denmark and Lord Lieutenant of Ireland. He died in The Tower of London (13th July 1683). Convicted of participation in a plot against the King and his brother, James, he is said to have commited suicide whilst a prisoner awaiting execution for treason. This official view was controversial at the time (see below).
His past experience may have influenced him towards taking his own life to protect his family. After his father’s execution his mother had to petition Parliament (1649), for return of their lands, which had been forfeit to the state on father’s execution..
When a child, he had allegedly been used as a hostage by the Parliametary side, at the seige of Colchester (1648), to encourage his father to surrender.
Arthur Capell, 1st Earl of Essex, portrait commemorating his appointment as Lord Lieutenant of Ireland in 1672
"1st EarlOfEssex 1672" by Sir Peter Lely - http://www.watfordmuseum.org.uk/cassiobury/galleries/arthur_capel2.html. Licensed under Public Domain via Wikimedia Commons - https://commons.wikimedia.org/wiki/File:1stEarlOfEssex1672.jpg#/media/File:1stEarlOfEssex1672.jpg
The Capel Family, by Cornelius Johnson (Jonson or Jonson van Ceulen), oil on canvas, circa 1640, National Portrait Gallery, London, NPG 4759. Provenance: purchased with help from The Art Fund, 1970.
The people in the portrait are (from left to right): Arthur Capel, 1st Earl of Essex (1631-1683) his father Arthur Capel, 1st Baron Capel (1604-1649) Henry Capel, 2nd Baron Capel (1638-1896) mother Elizabeth, Lady Capel (died 1661) Charles Capel (died 1657) Elizabeth Countess of Carnarvon (1633-1678) Mary Duchess of Beaufort (1630-1715).
Note:- See - Lady Capel’s Petition to Parliament (1649) for the return of her sequestrated lands