Union Grove, at the junction of U.S. Highway 271 and Farm Road 1844, eleven miles south of Gilmer in southern Upshur County, was first settled in the mid-1880s. Among the earliest settlers was John O'Byrne, a native of Ireland, who built a large plantation home and opened a sawmill. Around 1886 a school began operating near the O'Byrne house, but two years later the school building was moved to a site three miles north of Gladewater on the Gilmer Road. The school was part of the West Mountain district until 1907, when the districts were separated. The settlement remained small until the early 1930s, when oil was discovered nearby. Union Grove became a boomtown. By the mid-1930s it had two churches, a school, and a number of stores. The school had an enrollment of nearly 400 in the early 1940s. After World War II most of the businesses closed, but in the mid-1960s Union Grove still had a high school and a large number of houses. In 1990 the town had a population of 271; many of the residents commuted to work in nearby Gladewater or Longview.