MIDDLESEX was recorded in the Domesday Book as being divided into the six hundreds of Edmonton, Elthorne, Gore, Hounslow (Isleworth in all later records), Ossulstone and Spelthorne. The City of London, which has been self-governing since the thirteenth century, was geographically within the county, which also included Westminster, which had a high degree of autonomy. Of the six hundreds, Ossulstone contained the districts closest to the City of London. During the 17th century it was divided into four divisions, which, along with the Liberty of Westminster, largely took over the administrative functions of the hundred. The divisions were named Finsbury, Holborn, Kensington and Tower. The county had parliamentary representation from the 13th century. The title Earl of Middlesex was created twice, in 1622 and 1677, but became extinct in 1843.

The economy of the county was dependent on the City of London from an early time and was primarily agricultural. All manner of goods were provided for the City, including crops such as grain and hay, livestock and building materials. Tourism in early resorts such as Hackney, Islington and Highgate also formed part of the early economy. However, during the 18th century the inner parishes of Middlesex started to function as suburbs of the City and were increasingly urbanised.

The introduction of radial railway lines from 1839 caused a fundamental shift away from agricultural supply for London towards large scale house building. Tottenham, Edmonton and Enfield in the northeast developed first as working class residential suburbs with easy access to central London. The line to Windsor through Middlesex was completed in 1848, to Potter's Bar in 1850 and the Metropolitan and Metropolitan District Railways started a series of extensions into the county in 1878. Closer to London, the districts of Acton, Willesden, Ealing and Hornsey came within reach of the tram and bus networks, providing cheap transport to central London.

Following World War I, the availability of labour and proximity to London made areas such as Hayes and Park Royal ideal locations for the developing new industries. New jobs attracted more people to the county and the population continued to rise.

Source: http://en.wikipedia.org