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.