Mingo County, created on January 30, 1895, from the southern part of Logan County, is the youngest county in West Virginia. It lies on the Tug Fork between McDowell and Wayne counties, with a territory of 423.9 square miles. It is also bordered by Wyoming, Logan, and Lincoln counties, and by Pike County, Kentucky, and Buchanan County, Virginia. Mingo County lies in the heart of Appalachia. It is named for the Mingo Indians, for whose best-known chief, Logan, the mother county was named.

Mingo County was created after the population of the Tug Valley boomed with the construction of the Norfolk & Western (N&W) Railway through the region. Williamson is the county seat. Other principal towns include Delbarton, Matewan, and Gilbert. Mingo County is drained by the Tug Fork and the Guyandotte River and their tributaries, and the headwaters of Twelvepole Creek. The county is served by U.S. 119 (Appalachian Corridor G), U.S. 52, and several state and county routes, and by the Norfolk Southern Corporation, the successor to the N&W.

The first settlers of European descent were farmers who entered the Tug Valley about 1800. They were largely of English, Scotch-Irish, and German origins. They were followed much later by those who came to mine the coal and build the railroads of the industrial era. These newcomers, arriving in the late 19th and early 20th centuries, brought a wide ethnic diversity to the new county. They included Italians, Russians, Poles, Czechoslovakians, and African-Americans, as well as Jews, Greeks, Lebanese, and others.

Mingo County has vast coal deposits. Commercial mining began with the arrival in 1890 of the N&W, which established a major rail yard at Williamson. The early mines were underground mines. Deep mining continues, but in recent decades there has been a shift toward surface mining in Mingo County, including mountaintop removal mining. Mountaintop removal has been controversial due to the altering of the terrain and the filling in of streams and valleys after the extraction of the coal. Some say that the practice has aggravated recent flooding of the region. Its defenders point out that this mining method has created flat land which is being used for economic development such as an industrial park and a prison.

Loggers, who had floated timber down the Tug in earlier years, also increased their efforts with the arrival of the N&W, building branch lines into the woods and soon harvesting the county's virgin forests.

Mingo County was still part of Logan County when the infamous Hatfield-McCoy Feud occurred. Most of the Hatfields resided in what became Mingo County, where they farmed and timbered and were politically active, and many of the feud's key events took place within the present county. The main part of the feud began in 1882. A total of 13 people were killed as the conflict continued into the 1890s. Several Hatfield partisans were jailed, and one, Ellison "Cottontop" Mounts, was hanged in Kentucky. The vendetta died down after that. It became notorious due to the sensational publicity given it by the regional and national press.

Mingo County participated violently in the Mine Wars of the early 20th century. Matters came to a head in Matewan in May 1920, when police chief Sid Hatfield confronted agents of the Baldwin-Felts Detective Agency who had been evicting striking miners from local company-owned houses. A gun battle ensued, leaving ten people dead, mostly detectives. This shootout, which came to be known as the Matewan Massacre, was part of a chain of events leading up to the Battle of Blair Mountain in Logan County the next year, the largest armed uprising in America since the Civil War.

Despite the strains of change, Mingo prospered with industrialization. Matewan had opened a hospital in 1905, and Williamson Memorial Hospital was founded in 1918. County population increased from 11,359 in 1900 to 19,431 in 1910, peaking at 47,409 in 1950. Then the population fell because of the mechanization of coal mines and other causes, including regional job losses due to the shift of the N&W from coal-fired steam locomotives to diesel. In 2020, the county’s population was 23,568, its lowest total since 1910. By 2021, only 228 people were working in the Mingo County coal industry, and nearly all of its production was from surface mines.

The Tug and Guyandotte rivers flood occasionally, sometimes doing great damage to Mingo County. The most devastating recent floods occurred in 1977 and 1984, causing the loss of many homes and the demise of many businesses in the riverside communities of Williamson, Matewan, Kermit, and Gilbert. The R. D. Bailey Lake and Dam was completed on the Guyandotte in 1980 as a flood-control project, and floodwalls were built at Williamson (1991) and Matewan (1996) to protect those towns from the Tug.

The local school system is operated by an elected county board of education. Williamson has a campus of Southern West Virginia Community and Technical College. Southern began as a branch of Marshall University in 1969, becoming a community college when the state established the community college system. It offers associate degrees and provides education and training programs for local companies.

Prominent among Mingo County's recent citizens has been industrialist James H. "Buck" Harless of Gilbert, who parlayed small truck mines and sawmills into multimillion-dollar companies. The Discovery Channel and the Learning Channel were founded by John Hendricks, who was born in Matewan. The Dingess area produced Baltimore stripper Blaze Starr. Retired Gen. Robert "Doc" Foglesong was chief of U.S. Air Force operations in Europe. Don Blankenship was the chief executive officer of Massey Energy (later acquired by Alpha Natural Resources), a leading producer of coal. Elliott Maynard is a former justice of the West Virginia Supreme Court of Appeals.

Mingo County is still dependent on coal and its related industries; however, the tourism industry is emerging. The completion of four-lane Appalachian Corridor G (U.S. 119) has opened the county to visitors from north and south. Important developments include the Hatfield-McCoy Trail and the West Virginia Mine Wars Museum in Matewan. Additional tourism projects include the annual Hatfield-McCoy Reunion and Marathon, the King Coal Festival, and preservation of the Matewan Historic District as a National Historic Landmark.

In 2023, Adams Fork Energy and its partners announced a multi-billion-dollar clean ammonia production facility on a reclaimed mining site near Gilbert Creek. Construction, expected to begin in 2024, would employ some 2,000 workers. Later in the year, however, CSX separated from the project, placing its future in jeopardy.

In 2023, Mingo County's largest employers were the county school system, Mingo Logan Coal Company, Coalfield Community Action Partnership, West Virginia Personnel, and the Williamson Health & Wellness Center