[5][6] During the Civil War, the Battle of Johnsonville was fought for two days in the western half of the county in November 1864.

The remnants of the battle site are preserved and interpreted at Johnsonville State Historic Park.

But much of the battlefield has been submerged by Kentucky Lake, created by dams on the Tennessee River for flood control.

On the morning of August 21, 2021, storms riding along a stationary front in western Middle Tennessee produced widespread flash flooding across the counties of Stewart, Houston, Dickson, Hickman, and Humphreys.

Especially hard hit were the towns of McEwen and Waverly, where many homes and businesses were destroyed by floodwaters along Trace Creek.

Like most other counties in Middle Tennessee, Humphreys is historically a Democratic stronghold: it voted Democrat in almost every US presidential election up until 2004, making exceptions for Independent segregationist George Wallace in 1968 and Republican landslide winner Richard Nixon four years later.

However, like other rural Middle Tennessee counties, Humphreys is nowadays solid ground for the Republican Party, with the GOP margin of victory dramatically increasing in each presidential election since John McCain's narrow win in 2008.