North Fork of Long Island (Google Maps)
If you ask Google Maps to show the North Fork you get a highlighted area that includes most of the Town of Southold plus some bits of the Town of Riverhead. But neither Plum Island nor Fisher's Island.
Suffolk County, within which the North Fork is situated, has its own view of what makes up the North Fork suffolkcountyny.gov/Departments/Parks/Visit. This view is probably the most authoritative.
The North Fork of Long Island AVA is an American Viticultural Area (wikipedia.org/wiki/North_Fork_of_Long_Island_AVA). According to the history in the Wikipedia page it was established in 1985, just as winemaking began to take off in the North Fork area.
The AVA includes the townships of Riverhead, Shelter Island, and Southold.
Here is what Google Maps shows when asked to display Southold township. Both Plum Island and Fishers Island are correctly shown as part of the Town of Southold.
Plum Island is owned by the United States government and was the home of the Plum Island Animal Disease Center from 1954. It is closed to the public, with access controlled by the Department of Homeland Security.
Southold Township (Google Maps)
Fishers Island is also part of the Town of Southold (https://en.wikipedia.org/wiki/Fishers_Island,_New_York), though only accessible by ferry from New London, Connecticut, or by private boat. And Southold Town has recently assumed responsibility for policing Fishers Island (https://suffolktimes.timesreview.com/2023/11/town-now-patrols-fishers-island/) from the State Police.
Updated 2025-04-24 MDD