It is bordered by the Allegheny Mountains, from which the county derives its name, and it is the northernmost part of the Roanoke Region.

[3] At the time, the majority of the population lived around Covington, and the primary cash crop then was hemp, which was used for rope production.

However, as hemp demand and prices declined, the farmers of Alleghany switched to grain, hay and livestock production.

[4] During the American Civil War, the iron for the CSS Virginia (Merrimac) came from Longdale Furnace in the county.

Alleghany County is one of the 423 counties served by the Appalachian Regional Commission,[8] and it is identified as part of "Greater Appalachia" by Colin Woodard in his book American Nations: A History of the Eleven Rival Regional Cultures of North America.

The article includes geographic data from before and after the reincorporation of Clifton Forge as a town into the county.

In the 2020 United States presidential election, the county gave Republican candidate Donald Trump the highest margin, just under 45 percent, since the 1928 United States presidential election when Republican candidate Herbert Hoover won by over 45 percent.

The county economy is dominated by WestRock, which operates a paperboard mill in Covington, the second largest on the East Coast and an extrusion and converting facility in Low Moor.

Clifton Forge serves a major locomotive fuel facility for CSX Transportation.

The county also contains one Virginia state governors school, the Jackson River Governor's School; one technical center, the Jackson River Technical Center; and the Mountain Gateway Community College.