[2] Originally referred to as "East of Islip", the name was acquired in 1890 from the estate of William Nicoll, an English aristocrat who purchased the surrounding land in 1683 to erect a family residence.

Nicoll's purchase comprised 51,000 acres (210 km2) from the Secatogue Indians, reaching as far as Bayport to the east, Babylon to the west and Ronkonkoma to the north.

His mansion, Islip Grange, named after his family's ancestral estate at Northampshire, England, stood near the shoreline of what is now Heckscher State Park.

East Islip, as well as many hamlets along Long Island's south shore, was once an enclave for some of the nation's wealthiest families.

Some estate and early farmlands were donated to the Roman Catholic church and make up the current grounds of St Mary's of East Islip, which includes a private elementary and middle school, in addition to church and other parish buildings.

[3] It is the home of an experimental shellfish hatchery operated by the Town of Islip, near the town-operated public beach on the bay.

Two additional marinas are operated in Great River within the grounds of the Timber Point Country Club, the site of East Islip's only golf course.