You are probably thinking of Tangier Island in the Chesapeake Bay.
There’s also the Gullah dialect of the South Carolina-Georgia coast, it’s a black dialect that preserves some very old English forms.
Well this series came out like almost 20 years ago so it’s a somewhat vague memory. I do remember it wasn’t just blacks that they were referring to in fact it’s probably mostly whites or maybe it is that island in the Chesapeake Bay you just mentioned.