Middlesex is the smallest of England's historic counties by area, bounded by Hertfordshire to the north, the Thames to the south, dividing it from Surrey, the River Colne to the west, marking the border with Buckinghamshire, and the River Lea to the east, dividing it from Essex. Eighteenth-century surveys measured it at scarcely twenty-four miles long and eighteen broad, containing only 247,000 acres — yet because it contained the twin cities of London and Westminster in its south-eastern corner, Middlesex was, without serious rival, the wealthiest and most populous county in England, its market towns and hundreds administering a population that dwarfed every other shire.
Outside the metropolis itself, antiquarian writers described a pleasant, healthy county on light gravelly soil, its market gardens and meadows so heavily enriched by the vast quantities of manure and compost carted out from London that the whole cultivated countryside could fairly be described as one continuous garden, supplying the capital with fruit, vegetables and dairy produce. Villages such as Twickenham, Highgate and Hampstead, still genuinely rural in character, had already become fashionable retreats for wealthy Londoners seeking clean air within easy reach of town.
Within London and Westminster themselves lay a concentration of antiquities without equal anywhere else in the historic county system: Westminster Abbey and Hall, the Tower of London, the Guildhall, and a great number of aristocratic town houses along the Strand, Piccadilly and St James's, many designed by architects such as Inigo Jones and Christopher Wren. Hampton Court Palace on the Thames and Syon House near Isleworth extended this concentration of royal and noble building out along the river to the county's western edge. Middlesex's identity as a separate administrative county was finally absorbed into Greater London in 1965, but its name survives in institutions, postal addresses and the ceremonial memory of the historic county that once contained the nation's capital.