What is the name of the state that separated itself from another state in 1861 when the larger state joined the Confederacy?

West Virginia was once part of

Virginia. When Virginia declared secession from the United States

to become part of the Confederacy, the counties in northwestern

Virginia voted to secede from Virginia and remain loyal to the

United States. That area of Virginia became West Virginia. West

Virginia became the 35th U.S. state on June 20, 1863.