Thank -you Earl for contributing this information.

Island 81 is now part of mainland Arkansas in Chicot County. Across the river just north of Greenville MS. Google maps has it marked: https://maps.app.goo.gl/a24rejuiVDHdYugp7

It's now a flood plain with little development and I suspect the grave sites will have be washed away with the numerous flood in its history but I don't know that as a fact. The nearest cemetery of current record is Pleasant Green Cemetery just west of Island 81 inside the levee before Boggy Bayou. The river has changed course several times in the last 150 years and frankly I don't know if Pleasant Green was part of Island 81 during the war, but its a place to start.