St Albans Abbey claimed rights to the manor of Cashio (then called "Albanestou"), which included Watford, dating from a grant by King Offa in AD 793.
When Henry VIII dissolved the monasteries in 1539, Watford was divided from Cashio and Henry assumed the lordship of the manor of Cassiobury.
In 1546 he granted the manor to Sir Richard Morrison, who started building Cassiobury House with the extensive grounds (which were much larger than they are today, reaching as far as North Watford and southwards almost to Moor Park).
The Tudor mansion was completed by his son, Sir Charles Morrison, and boasted 56 rooms, a long gallery, stables, a dairy and a brewhouse.

In 1627 the estate passed into the Capel family through marriage.

Arthur Capell, 1st Earl of Essex, commissioned Hugh May to rebuild the Tudor house, c.1677–80, with sumptuous interiors created in collaboration with the wood carver Grinling Gibbons and the painter Antonio Verrio.
The park and gardens were laid out by Moses Cooke who devised woodland walks and avenues, and provided "an excellent collection of the choicest fruits".

Later, the gardeners George London and Charles Bridgeman also worked at Cassiobury.
Between 1672 and 1720 an avenue of 296 lime trees was planted, linking the gardens to Whippendell Wood; remnants can still be seen today.

In the late eighteenth century, parts of the Grand Union Canal passing through the property were widened and landscaped on the insistence of William Capell, 4th Earl of Essex, who sat on the board of the canal company.

C. 1799–1805, the 5th Earl of Essex commissioned James Wyatt to remodel the house in the Gothic style, and Humphry Repton to overhaul the park.
Later, a number of lodges and other buildings were constructed by Wyatt's nephew, Jeffry Wyatville; of these, only Cassiobury Lodge in Gade Avenue survives.
At this time the park comprised 693 acres (2.80 km²), the Home Park and the Upper Park being separated by the River Gade.
The Upper Park became the West Herts Golf Course.

In 1841 a fire destroyed the orangery, which was filled with newly collected plants and fine orange trees, some of which had been presented to the 6th Earl by Louis XVIII.
Herds of deer roamed the park.
Parties were a regular feature at the weekends.
The public were allowed to ride and walk through the grounds, but had to apply for a ticket in advance.
St Albans Abbey claimed rights to the manor of Cashio (then called "Albanestou"), which included Watford, dating from a grant by King Offa in AD 793. When Henry VIII dissolved the monasteries in 1539, Watford was divided from Cashio and Henry assumed the lordship of the manor of Cassiobury. In 1546 he granted the manor to Sir Richard Morrison, who started building Cassiobury House with the extensive grounds (which were much larger than they are today, reaching as far as North Watford and southwards almost to Moor Park). The Tudor mansion was completed by his son, Sir Charles Morrison, and boasted 56 rooms, a long gallery, stables, a dairy and a brewhouse.
In 1627 the estate passed into the Capel family through marriage.
Arthur Capell, 1st Earl of Essex, commissioned Hugh May to rebuild the Tudor house, c.1677–80, with sumptuous interiors created in collaboration with the wood carver Grinling Gibbons and the painter Antonio Verrio. The park and gardens were laid out by Moses Cooke who devised woodland walks and avenues, and provided "an excellent collection of the choicest fruits".
Later, the gardeners George London and Charles Bridgeman also worked at Cassiobury. Between 1672 and 1720 an avenue of 296 lime trees was planted, linking the gardens to Whippendell Wood; remnants can still be seen today.
In the late eighteenth century, parts of the Grand Union Canal passing through the property were widened and landscaped on the insistence of William Capell, 4th Earl of Essex, who sat on the board of the canal company.
C. 1799–1805, the 5th Earl of Essex commissioned James Wyatt to remodel the house in the Gothic style, and Humphry Repton to overhaul the park. Later, a number of lodges and other buildings were constructed by Wyatt's nephew, Jeffry Wyatville; of these, only Cassiobury Lodge in Gade Avenue survives. At this time the park comprised 693 acres (2.80 km²), the Home Park and the Upper Park being separated by the River Gade. The Upper Park became the West Herts Golf Course.
In 1841 a fire destroyed the orangery, which was filled with newly collected plants and fine orange trees, some of which had been presented to the 6th Earl by Louis XVIII. Herds of deer roamed the park. Parties were a regular feature at the weekends. The public were allowed to ride and walk through the grounds, but had to apply for a ticket in advance.
Cassiobury Park