Brookhaven and South Haven Hamlets are located in the southern part of the Town of Brookhaven in Suffolk County, NY. The Town of Brookhaven is the largest Town in land area in New York Statesee governmental units.
During much of the 19th century, Brookhaven was known as Fireplace; but this name has not been used since 1871 when it officially became Brookhaven. Because the hamlet is in the Town of Brookhaven, there is regular confusion between them—it's almost become a habit when describing where I live to make it clear that it's the hamlet!
As hamlets, Brookhaven and South Haven have no formal boundaries. All would say that they are bounded on the south by the Great South Bay and most would say that Brookhaven's western boundary is the Village of Bellport ; and that South Haven's eastern boundary is the Carman's River and Shirley. Brookhaven itself is bounded on the east by the lower reach of the Carman's River, the Wertheim National Wildlife Refuge, and the Hamlet of South Haven. South Haven and Brookhaven have long been closely associated communities, and from a historical perspective, I've treated them as one. Most residents would say that Brookhaven's northern boundary does not extend much north of the Sunrise Highway (NYS Route 27), especially since the Town Landfill can be found there—and that is, most assuredly, in the hamlet of Yaphank! South Haven, on the other hand, is usually considered to include all of the South Haven County park, which is north of Sunrise Highway—but it could be said to be, at least in part, in Yaphank.
Both hamlets are situated within the South Country School District. the district's high school and one of its elementary schools are located in the hamlet of Brookhaven, while another special school (the former South Haven district elementary school), is located in South Haven
The boundaries of the "Brookhaven" Post Office, 11719, are greater than the Hamlet and includes South Haven. So are the boundaries of the Brookhaven Fire District, the South Country Ambulance District, and the South Country School District (if you're not familiar with the oddity of special districts in New York State, none of boundaries of these districts make much sense today, nor are they contiguous.) There is also a Historic District for much of the hamlet of Brookhaven.