Fincastle was divided in 1776, with the western portion named Kentucky County, Virginia.

[5] In 1780, the Virginia legislature set aside all land in Kentucky County for soldiers who had served in the Revolutionary War.

During the Civil War, Magoffin County was a border county, with a moderate unionist majority existing in the area, albeit with highly divided sentiment.

[10] As the late 19th century progressed, Magoffin County became a leading supplier in oil and gas production in the area, with some of the first oil wells in Eastern Kentucky being built in the county.

There is a significant Melungeon or mixed race group of Carmel Indians in Magoffin County.

21.40% of all households were made up of individuals, and 8.20% had someone living alone who was 65 years of age or older.

Magoffin County prior to the 1930s was a strongly Republican County at the national level, voting for the Republican Party in an unbroken streak under the Fourth Party System from 1880 to 1932.

However at the state and local level it remained Democratic, voting for James B. McCreary in 1875, and Preston Leslie in 1879 for governor – both former Confederates.

It voted for Democrat Andy Beshear for Governor in both the 2019 and 2023 gubernatorial elections, but Republican for all other statewide offices.

The last active coal mine in Magoffin County closed in 2015.