Middlesex is one of the historic counties of England and the second smallest by area. The county once contained the rich and politically independent City of London on its southern boundary. The county was affected by the expansion of London in the 18th and 19th centuries. From 1855 the south east was administered as part of London. When county councils were initially introduced in England in 1889 around 20% of the area of Middlesex, and a third of its population, was transferred to the County of London.
In the interwar years urban London further expanded, with the expansion of public transport, and the setting up of new industries outside inner London.
After a Royal Commission on Local Government in Greater London, Middlesex was absorbed by an enlarged Greater London in 1965. Despite its disappearance as an administrative county, Middlesex is still used as an area name. It was kept as a postal county; it is an optional component of postal addresses. It is still regarded by many as a meaningful area, with its own teams in County cricket, rugby and other sports and pastimes.