Dangar Island is a forested island, 29 hectares (72 acres) in area, in the Hawkesbury River, just north of Sydney, New South Wales, Australia. Dangar Island is a suburb of Hornsby Shire and as at the 2011 Census had a population of 267, which swells dramatically during holiday seasons. The island is serviced regularly by the Dangar Island Ferry service that departs from Brooklyn and takes about ten minutes. Dangar Island has been known to the local Guringai Aborigines for thousands of years. The first European to visit the area was Governor Arthur Phillip, who explored the lower river by small boat in March 1788 within weeks of the First Fleet's arrival. He named it Mullet Island, for the abundance of fish in the local Hawkesbury River. At first the local people were friendly towards him, but when he returned a year later, they would not come into contact. By 1790, over half the Guringai people had succumbed to the smallpox the British had brought with them.

The island was purchased in 1864 and renamed by Henry Carey Dangar, the son of Henry Dangar,a surveyor, pastoralist and parliamentarian. Dangar leased the island to the Union Bridge Co of Chicago for the construction of the original Hawkesbury River Rail Bridge between 1886-1889. About 400 Americans and their families lived there and the island boasted a large social hall, school, library and its own newspaper. In the 1920s the island, which is barely a five-minute walk across, was divided into residential plots, though space was reserved on the beach, the flat and the top of the hill for recreational use. Dangar Island Post Office opened on 1 September 1951 and closed in 1986.
A visit to the Island is truly worthwhile. The residents are very friendly and hospitable. All that remains of the home built by Henry Dangar is the stone water tower and The Pavilion.