Isleworth is a town sited within the London Borough of Hounslow in West London, England. It lies immediately east of the town of Hounslow and west of the River Thames and its tributary the River Crane. Isleworth's original area of settlement, alongside the Thames, is known as 'Old Isleworth'. The north-west corner of the town, bordering on Osterley to the north and Lampton to the west, is known as 'Spring Grove'.
Isleworth's former Thames frontage of approximately one mile, excluding that of the Syon Park estate, was reduced to little over half a mile in 1994 when a borough boundary realignment was effected in order to unite the district of St Margaret's wholly within London Borough of Richmond upon Thames. As a result, most of Isleworth's riverside is that part overlooking the 8.6-acre islet of Isleworth Ait: the short-length River Crane flows into the Thames south of the Isleworth Ait, and its artificial distributary the Duke of Northumberland's River west of the Isleworth Ait, one of two Colne distributaries constructed for aesthetic reasons in the 1600–1750 period.