Monongalia County was formed in 1776 when Virginia's remote District of West Augusta was divided into three counties: Ohio, Yohogania and Monongalia, all named for their most prominent rivers.

In 1780, in his Notes on the State of Virginia, Thomas Jefferson gave the militia enrollment of what was then the vast Monongalia County at 1,000 troops.

In 1863, West Virginia's counties were divided into civil townships, with the intention of encouraging local government.

This proved impractical in the heavily rural state, and in 1872 the townships were converted into magisterial districts.

[4] Monongalia County was divided into seven districts: Battelle, Cass, Clay, Clinton, Grant, Morgan, and Union.

[11] As of the 2010 United States census, there were 96,189 people, 39,777 households, and 20,032 families living in the county.

[12] In terms of ancestry, 25.7% were German, 17.1% were Irish, 13.0% were English, 11.0% were Italian, 7.5% were American, and 5.0% were Polish.

31.30% of all households were made up of individuals, and 8.40% had someone living alone who was 65 years of age or older.

Currently, these members are: Thomas Bloom (D),[17] Sean Sikora (R) and Jeffery Arnett (D).

[18] While still typically favoring Republicans, the county tends to lean significantly more Democratic than the rest of West Virginia.

In the 20th century, Monongalia County had been a bellwether for West Virginia, voting the same as the state in every election from 1916 to 2024, even as the candidate lost the national election, with the sole exception of 2008 when Barack Obama won the county and lost the state.

The rural precincts are slightly more populous, resulting in the county's Republican tilt.