Harmondsworth is a village in the London Borough of Hillingdon in the county of Greater London with a short border to the south onto London Heathrow Airport and close to the Berkshire county border. The village has no railway stations, but adjoins the M4 motorway and the A4 road. Harmondsworth was in the historic county of Middlesex until 1965. It is an ancient parish that once included the large hamlets of Heathrow, Longford and Sipson. Longford and Sipson have modern signposts and facilities as separate villages, remaining to a degree interdependent such as for schooling. The Great Barn and parish church are medieval buildings in the village. The largest proportion of land in commercial use is related to air transport and hospitality. The village includes public parkland with footpaths and abuts the River Colne and biodiverse land in its Regional Park to the west, once the grazing meadows and woodlands used for hogs of Colnbrook.

The London Borough of Hillingdon is the largest and westernmost borough in West London, England. It was formed in 1965 from the districts of Hayes and Harlington, Ruislip-Northwood, Uxbridge, and Yiewsley and West Drayton in the ceremonial county of Middlesex. Today, Hillingdon is home to Heathrow Airport and Brunel University, and is the second largest of the 32 London boroughs by area.