Historic county of England
Middlesex
Thames along the south, London across the centre, Colne and old countryside surviving west and north.
Middlesex is a compact Thames-side county whose landscape has been transformed more completely by London than almost any other. Urban development now covers most of the county, spreading through older towns and villages towards the Colne valley in the west and the higher ground along its northern edge.
Yet Middlesex has not disappeared beneath the conurbation. Its underlying structure survives in the Thames, Lea and Colne corridors, in commons, parks, reservoirs and river meadows, and in the continuing identities of its older settlements. Middlesex is therefore not a relic of a vanished rural landscape: it is a living geographic county whose modern character happens to be overwhelmingly urban.
- Kingdom of Middle Saxons
- County by 7th–8th century
- 'The Capital County'
- Listed in Domesday Book
- Two cities – London and Westminster
- Name from Old English Middelseaxe
County geography
Current Census
Contemporary Census profile
England and Wales Census 2021. Detailed contemporary statistics are available in the Geographic County Census Explorer.
- Population density
- 14,940.5 people per sq mi (5,768.6 people per km²)
- Population
- 4,256,764
A county transformed by London
London expanded across Middlesex over several centuries, eventually joining once-separate towns and villages into almost continuous urban country.
That process changed land use on an extraordinary scale, but urban growth does not erase county geography. Middlesex remains the territorial layer beneath the metropolitan landscape.
Rivers still show the frame
The Thames forms Middlesex’s great southern edge, while the Colne defines much of the western side and the Lea provides the principal eastern river corridor.
These waterways remain among the clearest ways to understand the county. Even where buildings dominate, river valleys, floodplains and reservoirs preserve an underlying physical structure.
Green Middlesex
Despite its intensely urban character, substantial open landscapes survive. The Colne valley retains wetland and meadow country; commons and woodland interrupt the northern suburbs; and major parks preserve large green spaces beside the Thames.
This surviving openness makes Middlesex more geographically varied than its metropolitan reputation suggests.
County questions
Questions about Middlesex
Does Middlesex still exist?
Yes. Middlesex remains a geographic county. The abolition of Middlesex County Council and the creation of Greater London altered local government, not the county itself.
Did Greater London replace Middlesex?
No. Greater London is a later administrative area extending across several geographic counties. It did not abolish or redraw Middlesex.
County record
Names and continuity
- Formal name
- County of Middlesex
- Name note
- Kingdom of the Middle Saxons
- County day
- 16 May
- Foundation
- County by 7th–8th century
- Earliest reference
- Listed in Domesday Book
Middlesex and County of Middlesex are forms of the county name. The name means the territory of the Middle Saxons and is recorded centuries before the Norman Conquest.