With the blessing of the local historical society--Potton Heritage Association/Association du patrimoine de Potton--the current Cemetery Caretaker is John Cogan of nearby Newport, Vermont.
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This was an abandoned and overgrown cemetery on chemin de la Vallée Missisquoi next to the Carrefour des Campeurs Campground. Restoration of the cemetery began in July 2013. More details will be added.

While recently working in the cemetery, local resident John Aiken stopped to look at progress. He stated that when he was a boy, the land that the cemetery sits on was part of "the Sargent farm," and that the cemetery was not overgrown. The Sargent family used to have their cows graze the cemetery as apparently was a common practice in this area at that time. The Sargents had family buried in this cemetery.

Former Mansonville & Dunkin Postmaster Kenneth Jones had this to say about the cemetery: "...the 'Gilman' so called for being situated near the establishment of Dr. Gilman and his father, Thomas Gilman, who came to Potton about the year 1800. There are probably seventy-five or more bodies mouldering in the dust where good intentions have been overtaken by procrastination... The Gilman Stones have been brought up to Mansonville... "

The oldest burial listed is an infant in 1819.
The most recent burial listed is 1931.
There were just a handful of 20th-Century graves.

Information mentioned in comments has come from these sources:

JC = John Cogan
KJ = Kenneth Jones, Former Mansonville & Potton Postmaster
PD = Peter Downman, Historian of Mansonville Area
MS = Marlene Simmons & Paul Jennings, Genealogists
JC = Joan Cruickshank, Genealogist
MD = Marilyn Davis & Marjorie-Anne Smith, Genealogists
SJ = Sandra Jewett, Historian & President of PHA
LML = Legion Memorial Library/Bibliothèque de Mansonville
PHA = Potton Heritage Assn/Association du patrimoine de Potton
BCH = Brome Co. Hist. Soc./Société Historique du Comté de Brome