The origin of the place name Gilgo on Long Island's South Shore does seem
to be obscure.  According to Karl Proehl and Barbara Shupe's Long Island
Gazetter there are several place names near the western part of the Great South
Bay that bear the name "Gilgo."  The oldest appears to be Gilgo Inlet, which I
have found just to the east of Jones Inlet on a Coast Survey manuscript map
dated 1835.  The Coast Survey set up a station for triangualtion named "Gilgo"
next to the inlet.  I have not been able to identify this inlet on any earlier
map, but B.F. Thompson in the 1843 edition of his history of Long Island states
(p. 451) that it was earlier known as Huntington Gut, which opened up up around
1766 (?).  A quick check of property maps and the indexes of county histories
does not turn up the name "Gilgo" in the area.  It seems just possible that the
inlet might have been named in honor of someone by the Coast Survey.