The Village of Roslyn Harbor was incorporated at the same time that the adjacent Village of Roslyn was incorporated. The owners of the estates in Roslyn Harbor established a separate village as they felt their needs were different from those of the inhabitants of the more densely populated Village of Roslyn.1
Beginning in the 1830s Roslyn Harbor's picturesque shoreline was recognized as a rural retreat for wealthy New Yorkers. From that time until c. 1930, the community's farmhouses and farmland were transformed into large country estates by New Yorkers seeking weekend and summer retreats from the city.
The small village of Roslyn Harbor, incorporated in 1931, covers an area of approximately 670 acres and in 2019 had 378 homes and a population of about 1108 with about 802 in the Town of North Hempstead and 306 in the Town of Oyster Bay.
The era of "estate" incorporation came to an end in 1936, when a new Nassau County charter preserved the rights of villages already incorporated to legislate local zoning laws but denied it to newly incorporated villages. Accordingly, there has not been any incorporation of villages in the town of North Hempstead since 1936. 
Roslyn Harbor is almost exclusively a suburban residential community and only a few large original estates remain, especially along Hempstead Harbor.
The Village of Roslyn Harbor lies in Nassau County in both the town of Oyster Bay and the town of North Hempstead. It is part of both the Roslyn and North Shore School Districts.
There are many sites to see in Roslyn Harbor, most notable:
Cedarmere – https://www.friendsofcedarmere.org
In 1843 poet and New York Evening Post editor, William Cullen Bryant, purchased 40 acres and established his estate, which he named "Cedarmere." With scenic views of Hempstead Harbor, Cedarmere was his beloved estate which he considered his retreat from his busy New York life.
Click here to see current events going on at Cedarmere.
Nassau County Museum of Art- https://nassaumuseum.org
Ranked among the nation's most important suburban art museums, the museum of Art is located 25 miles east of New York City on the former Frick "Clayton" Estate. This 145-acre property is located in Roslyn Harbor and comprises more than 20% of the Village. The land that eventually became the museum grounds was previously the undeveloped portion of Cedarmere.