Department of Key West, was a military department of the Union Army created on February 1862 from the Department of Florida. It had command over the posts that were newly captured by “Expeditionary Corps” combined of Army and Navy units under Brigadier General Thomas W. Sherman and Flag Officer Samuel Francis Du Pont. These were posts at Fernandina, St. Augustine and the forces investing Fort Pulaski and blockading the Savannah River on Tybee Island at the mouth of the river.