Locust Grove is a hamlet and former census-designated place (CDP) in the Town of Oyster Bay in Nassau County, on Long Island, in New York, United States.

It is located within the CDP of Syosset, which absorbed it for the 1990 United States Census.

[3] According to the United States Geological Survey, Locust Grove is located roughly 197 feet (60 m) above sea level.

[1] At the time of the 1960 United States census, the population of Locust Grove was 11,558.

[1][6][7] Additionally, in 1990, the Long Island Lighting Company (LILCO) estimated the total population to be 9,060, as of January 1 of that year.