To the northwest of Cassiobury, outside the Borough of Watford in the Three Rivers District, is The Grove, the former estate and house of the Earls of Clarendon.

The house, which originally dated from the reign of Queen Elizabeth I, contained lavishly decorated interiors and a substantial art collection and was surrounded by landscaped park land.

With the extension of the Metropolitan Railway to Watford in 1926, residential development around the new Watford tube station grew rapidly as the homes of Metro-land were constructed over the site of the former Essex mansion, and Humphry Repton's landscaped vistas gave way to suburban lawns.

[2] Although the Essex mansion house no longer exists, traces of the area's noble past remain; the Cassiobury House stable block (built c. 1805–1815) still stands on Richmond Drive; now called Cassiobury Court,[3] the buildings have been Grade II listed[4] and are now used as a drug rehabilitation centre.

[5] Several residential street names recall former Earls of Essex; Coningesby Drive, Devereux Drive, De Vere Walk and Capelvere Walk all bear names of former Lords of Cassiobury House.