Union is a town in Monroe County, West Virginia, United States. The population was 548 at the 2000 census. It is the county seat of Monroe County. Union was so named because in frontier days, the site of the town was a rendezvous for troops during the Indian Wars. It was settled by James Alexander in 1774 and originally charted in 1799. Located east of Union is Rehoboth Church, the oldest Methodist church in West Virginia.