The ancient boundaries of the county were the rivers Colne, Lee and Thames, and a ridge of hills. It initially included the wealthy and politically independent City of London in the south. The City of London became a county in its own right and although separate, dominated the early administration of Middlesex.
The generally low-lying county was the second smallest by area in 1831.
Because of the proximity of London the population was unusually high for an English county — approaching three million in 1881 — which caused problems for the administration of local government and justice. In the 18th and 19th centuries the population density was especially high ...