Barbour County was created from parts of Lewis, Harrison, and Randolph counties by an act of the Virginia legislature on March 3, 1843. The county was named for the distinguished Virginia jurist Philip Pendleton Barbour, as was the county seat, Philippi. Settlement began as early as 1780.

Barbour County has an area of 342.9 square miles with a population of 15,465 in 2020. It is located on the Allegheny Plateau in north-central West Virginia. Its mountainous terrain is drained by the Buckhannon, the Middle Fork, and the Tygart Valley rivers. U.S. 119 and U.S. 250 run north and south the full length of the county, while U.S. 33 cuts across its southernmost tip. It is bordered on the north by Taylor and Preston counties, on the east by Tucker and Randolph, on the south by Upshur, and on the west by Harrison. Laurel Mountain, the westernmost of the high Allegheny ridges, forms the eastern boundary of Barbour County.

The 2020 population of Philippi, the county seat, was 2,928. The town is located on the Tygart Valley River at the junction of U.S. 119 and U.S. 250, in the center of the county. Philippi's historic covered bridge carries U.S. 250 across the river. It was designed and built by Lemuel Chenoweth in 1852. Barbour has another covered bridge, as well, crossing the Buckhannon River at Carrollton.

Belington, the second-largest town in Barbour County, is located on U.S. 250 ten miles southeast of Philippi. It was named after John Bealin, who established a store there before the Civil War. Its 2020 population was 1,804. Both Philippi and Belington were sites of battles during the first campaign of the Civil War.

Before dawn on June 3, 1861, what is generally considered the first land battle of the Civil War among organized troops took place at Philippi as 3,000 federal troops under Col. Benjamin F. Kelley routed a newly recruited and poorly equipped Confederate contingent of about 800, commanded by Col. George A. Porterfield. While no one was killed during the brief encounter, both sides suffered casualties. The Battle of Belington or Laurel Mountain was a series of skirmishes that took place the following month, July 7-11, 1861. Federal troops under Brig. Gen. William S. Rosecrans attacked a nearly equal number of Confederates commanded by Brig. Gen. Robert S. Garnett and drove them from their positions on Laurel Mountain.

Until the late 20th century the economy of Barbour County was based primarily on its natural resources, including coal, gas, and timber, as well as agriculture. Historically, the county's agricultural production has come from family farms nestled among the mountains and along the river valleys. At the beginning of the 20th century there was a large hardwood timber industry. Loggers soon exhausted the great stands of virgin timber, although second- and third-growth timber is still harvested annually. Logging and wood products remain important industries.

Oil and coal no longer contribute as greatly to the county's economy as they did a century ago. The oil reserves were largely depleted early in the 20th century, and the coal industry has experienced a decline from its peak production of 3,895,803 tons in 1948 to just more than 2.3 million tons in 2021, making it the state’s 13th leading coal-producing county. In 2023, the largest employers in Barbour County (most to fewest employees) were Arch Coal, Hometown Care, the county school system, Century Mining, and Davis Health System

The history of Alderson Broaddus University in Barbour County dates from 1909 when Broaddus Institute moved from Clarksburg to Philippi. It was merged with Alderson Academy in 1932 and became a four-year coeducational college. The private Baptist school had recognized programs in nursing, the medical sciences, education, music, and the liberal arts. It was the first college in West Virginia to offer a four-year degree in nursing. It became a university in 2013 but closed permanently in 2023 due to financial struggles.

Among the prominent people of Barbour County were the Dayton and Woods families. The Daytons were active in the formation of West Virginia, while a member of the Woods family was a delegate to the Virginia secession convention in 1861 and voted for secession. U.S. District Judge Alston G. Dayton authored a historic legal decision in the 1907 Hitchman case, which sanctioned the yellow-dog contract and the use of court injunctions as anti-union devices during the period of the West Virginia Mine Wars. Under the leadership of Ruth Woods Dayton the two families joined in founding the Daywood Foundation, a philanthropic organization based in Charleston. Judge Ira Robinson was also an important West Virginia jurist. His house, Adaland, near Philippi, is now open to the public. Ida L. Reed composed hundreds of religious hymns, including "I Belong to the King." Howard Willis Smith was a noted artist and cartoonist, and Ted Cassidy played "Lurch" on the television comedy, The Addams Family.