Perhaps, these links may provide some sort of clue for you..Good Luck..
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http://www.illinoishistory.com/westillinoislegends.html

EXCERPT:

Smallpox Island, in the Mississippi opposite Alton, was used as a burial site for Confederate POWs who perished while incarcerated in Alton's military prison (see my "New Light On Smallpox Island," Springhouse, Volume 7, Number 4). As one might expect considering its sordid history, the island is the scene of a number of ghost stories, some of them quite grim. The following yarn was told to me as a child by my great-uncle, the late Joe Dromgoole of the Alton Telegraph. Like many oldtime Irish-Americans, Uncle Joe had a real flair for stories, a gift never more obvious than in this tale.
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http://www.springhousemagazine.com/v7n4/smallpox.htm

EXCERPT:

The portion of the Tow Head [yet another name for Sunflower/Smallpox Island] acquired by the Corps of Engineers in fee simple, parcel S-2-A, now holds the south abutment of lock and dam 26; it is believed to be the same portion of the Tow Head employing the greatest use over the years; the area that held the smallpox hospital .... Today a picnic area shaded by taR cottonwoods hes on either side of the levee ... A walk east along the levee on land covering the sluice that once separated the islands [i.e., Sunflower and Ellis] leads to the railroad. The track is heavily fined with wild grape, trumpet vine and elderberry-the only sounds, the rushing of the water's flow, songs of birds, buzzing of bees.
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http://www.historicmarkers.com/tag/dedication/10/20/

EXCERPT:

Smallpox Island MO99

A monument that honors the 233 confederate prisoners of war and 16 civilians who died of the disease on the vanished island.
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Gay