During the 1920s the civil parish bore a rapid, planned increase in population and housing, and was absorbed by Uxbridge Urban District in 1929.

When a local board of health was created for Uxbridge, the western part of Hillingdon parish was included within it.

[6] Under the Local Government Act 1894, Hillingdon parish was divided in two along the boundary of the board of health district.

The A40 (Western Avenue) was rerouted in the early 1990s to run slightly north of its original route, thereby allowing traffic to flow without interruption at the junction of Hillingdon Circus.

[7] Hillingdon is a traditional Conservative stronghold lying within the Uxbridge and South Ruislip constituency, represented from 2015 until 2023 by Boris Johnson.

Before that, John Randall MP had represented the constituency since 1997, following the death of fellow Conservative Sir Michael Shersby.

[11] The church of St John the Baptist stands at the top of Hillingdon Hill, at its junction with Royal Lane.

[14] There is a notable brass on the north wall of the south aisle dedicated to John, 8th Baron Strange of Knokin and his wife Jacquetta (1509).

[17] Hillingdon Court was built in 1858 by Sir Charles Mills as his family home, after he had bought separate adjacent properties in Vine Lane.