Harmondsworth was originally a parish, with the name first recorded in AD 780 when King Offa granted land to his servant Aeldred. It was mentioned in the Domesday Book, its name coming from the Anglo-Saxon Heremodes worþ, meaning 'Heremod's enclosure'.
The church of St Mary within the village has with parts dating from the 12th century. The Grade I listed Harmondsworth Barn, Britain's largest tithe barn, made entirely without nails.
There are two UK Border Agency immigration removal centres in Harmondsworth. British Airways is headquartered in Waterside in Harmondsworth. The building officially opened in 1999.