Middlesex is one of the 39 historic counties of England being the second smallest (after Rutland). When county councils were introduced in England in 1889 part of Middlesex was used to form the County of London and the remainder formed the administrative county of Middlesex. By 1965 urban London had further expanded and almost all of the original area was incorporated into Greater London. Middlesex is still used informally as an area name and may be included in some postal addresses.