Great River is a hamlet and census-designated place (CDP) located in the Town of Islip, Suffolk County, New York, United States. As of the 2010 census, the population of Great River was 1,489.
For centuries, the Algonquin people inhabited Long Island. A sub-division of the Algonquins known as the Secatogue tribe occupied all of the area in what is now the town of Islip. Their principal villages were at West Islip (Secatogue), Bay Shore (Penataquit), and Oakdale (Connetquot).On November 29, 1683, William Nicoll (Nicolls), founder of the Town of Islip and son of New York City Mayor Matthias Nicoll, was awarded the first royal patent to the east end of what is now the Town of Islip. Nicoll purchased land from Sachem (Chief) Winnequaheagh of Connetquot. He named his 50,000-acre (20,000 ha) plantation (an 8-by-10-mile (13 by 16 km) tract of land) "Islip Grange", in honor of his ancestral home of Islip in East Northamptonshire, England, from which Matthias emigrated in 1664. Nicoll's domain extended from East Islip to Bayport and embraced the present-day communities of Sayville, West Sayville, Oakdale, Great River, Islip Terrace, Central Islip, Hauppauge, Holbrook, Bohemia, Brentwood, Holtsville, and a portion of Ronkonkoma.Great River hamlet was formerly known as Youngsport. Youngsport Village's name was changed to Great River in either 1870 or 1881.