"Hospital Island" or Upper Mark Island, as it is known in 2021, is an inhospitable one-acre island off Kehail Point which is territorially part of Westport Island.

Historian Fannie Chase, author of "Wiscasset in Pownalborough" published in 1941, referred to it as a "quarantine ground at the mouth of the Sheepscot for cholera," referencing Edgecomb town records.

Westport Island town ledgers indicate the island was also used as a quarantine station in the 1840s for smallpox. One such ledger entry on March 9, 1840 ordered payment "in favour of Wm. Greenleaf for twelve dollars --- it being for lumber furnished for a hospital house erected on Mark Island so called."