Harlington is a district of Hayes in the London Borough of Hillingdon and one of five historic parishes partly developed into London Heathrow Airport and associated businesses, the one most heavily developed being Harmondsworth. It is centred 13.6 miles (21.9 km) west of Charing Cross. The district adjoins Hayes to the north and shares a railway station with the larger district, which is its post town, on the Great Western Main Line. It is in the west of the county of Greater London and until 1965 it was in the south-west corner of the historic county of Middlesex.