Fort Myer is the previous name used for a U.S. Army post next to Arlington National Cemetery in Arlington County, Virginia, and across the Potomac River from Washington, D.C. Founded during the American Civil War as Fort Cass and Fort Whipple, the post merged in 2005 with the neighboring Marine Corps installation, Henderson Hall, and is today named Joint …Fort Myer is the previous name used for a U.S. Army post next to Arlington National Cemetery in Arlington County, Virginia, and across the Potomac River from Washington, D.C. Founded during the American Civil War as Fort Cass and Fort Whipple, the post merged in 2005 with the neighboring Marine Corps installation, Henderson Hall, and is today named Joint Base Myer–Henderson Hall.