[2] Its county seat is St. Clairsville, while its largest city is Martins Ferry.

Many of these people would become outspoken critics of slavery, including famous abolitionist Benjamin Lundy.

[5] At one time, steamships traveling down the Ohio River knew the county's community of Bellaire as the last stop for coal until Cincinnati.

[7] Given the county's transportation resources, fuel resource, and experienced workforce in nearby Wheeling, West Virginia, the county was an excellent location for a glass manufacturing plant.

[11] Belmont County was the venue for the world-famous Jamboree in the Hills outdoor country music festival from 1977 to 2018.

In 1986, the syndicated Paul Harvey Show featured a special election being held in Belmont County for purposes of selecting a new official county seal and flag, created by then-county resident Michael Massa.

Captina Creek flows eastward through the lower part of the county, discharging into the Ohio at Powhatan Point, and McMahon Creek also flows eastward through the center of the county, discharging into the Ohio at Bellaire.

The county terrain consists of low rolling hills, etched with drainages.

[13] The terrain slopes to the east,[14] with its highest point, Galloway Knob (1,396' or 426m ASL) at 1.2 miles (1.9 km) southeast of Lamira.

[16] As of the 2010 United States census, there were 70,400 people, 28,679 households, and 18,761 families in the county.

[23] In terms of ancestry, 26.0% were German, 17.9% were Irish, 12.4% were English, 10.1% were Italian, 9.0% were Polish, and 6.2% were American.

[26] As of the 2000 United States census,[27] there were 70,226 people, 28,309 households, and 19,250 families in the county.

20.2% were of German, 12.5% Irish, 12.0% American, 10.3% English, 10.2% Italian and 9.0% Polish ancestry according to the 2000 census.

As of 2019, Belmont County's elected commissioners are: Jerry Echemann (R), J. P. Dutton (R), and Josh Meyer (R).

[31] Belmont County is served by several detention centers located around St. Clairsville.

The Belmont Correctional Institution is located on 158 acres (0.64 km2) between St. Clairsville and Bannock on State Route 331.