Overthorpe, Double Bay, Heritage residence in Double Bay, Australia

Overthorpe is a former mansion in Double Bay whose gardens have retained rare Australian rainforest species and ornamental trees from the 19th century. The grounds showcase plant collections that were cultivated and expanded over decades.

The site was part of Sir John Hay's experimental garden, an unusual entry in the 1880 Sands Directory, before Overthorpe was built from 1900 to 1906. Hay, NSW Colonial Treasurer and vice-president of the Agricultural Society, lived at Rose Bay Lodge. The property was added to the State Heritage Register on 2 April 1999.

The site was part of Sir John Hay's experimental garden, listed unusually in the 1880 Sands Directory while he lived at Rose Bay Lodge. Hay's roles as vice-president of the Agricultural Society of NSW and of colonial exhibition commissions fit the 19th-century drive to cultivate experimental gardens. The garden held a gardener's cottage.

Overthorpe stands at 337-347 New South Head Road, Double Bay, on the eastern hill face that once formed Sir John Hay's garden, running from Ocean Street on the ridge west to Manning Street in the east. The site is a privately owned multi-unit residential complex, so the grounds are not open to the public; the buildings and former garden area are seen from the street. Edgecliff railway station lies about a ten-minute walk away.

The site was once part of Sir John Hay's experimental garden, which stretched from Ocean Street on the ridge to Manning Street. Hay, Colonial Treasurer and vice-president of the Agricultural Society of NSW, kept a gardener's cottage there, and the plot is believed to have held an experimental nursery. The 1880 Sands Directory listed the garden as an unusual entry while Hay lived at Rose Bay Lodge.