By 1839 the London to Harrow coach passed through Harlesden every day, and by 1855 an omnibus service to London ran from the Royal Oak inn. The village is recorded as having had a blacksmith, a grocer, and a shoemaker.
The first Railway appeared when the London & Birmingham (later the London & North Western Railway) built its first station to the south of the village on low lying land, in 1837.
Willesden Junction station opened in 1866 and ran six trains a day in each direction. There was another station, Kensal Green & Harlesden, half a mile to the west of the present Kensal Green station.
The railways encourage housing development, both quality housing and terraced cottages. In Harley Road the railway management built houses for its own workforce, and a series or parks and gardens were also planned, including the still existing Roundwood Park.
The All Souls' College Estates built Wrottesley Road in 1900 and leased surrounding land to builders of middle class housing. Later cheap houses were also built due to a crises in the housing market.
By 1920 there was continuous housing between Harlesden and Kensal Green, with some dairy farms still remaining in between.
The turn of the century was the heyday for Harlesden. The mainly middle class population enjoyed nine churches and chapels, including a Catholic convent in Crown Hill Road from 1886, with a girls' school from 1888, a court, a library, a sub-fire station, Roundwood Park, several cinemas and a telephone exchange. A clock was erected in 1888 to commemorate Queen Victoria's Jubilee the year before.
The High Street was rebuilt in the Edwardian period and the Willesden Hippodrome, a large music hall, opened in 1907. The same year saw the first electric trams in Harlesden. In 1912 Harlesden railway station was opened near the site of the old Willesden Station, and in 1917 electric trains to Watford began operating on this line.
With the railways came industry. By 1890 washing machines, bicycles and antiseptic fluids were being made here. McVities biscuit factory was nearby in East Twyford, there were three large factories in Acton Lane, including a power generation station.
This industrial growth led the middle classes to abandon Harlesden, and between the two World Wars Harlesden became an entirely working class area, with many living in poverty.
Although much of the area needed improvement, redevelopment did not start to any great extent until the 1970s. For example, prefabricated houses for the homeless after the war time bombings remained on Harlesden Road until the late 1960s.