In September 2018 The United States Office of Management and Budget (OMB) added Washington County to the Mobile, Alabama Metropolitan Statistical Area but was removed in effective July 2023.

In 1807 former U.S. Vice President Aaron Burr was arrested at Wakefield in Washington County, during his flight from being prosecuted for alleged treason (of which he was eventually found innocent).

Some members of these tribes stayed behind on their traditional lands in southwest Alabama, taking refuge in the forests and swamps.

In the 19th century, the county was largely developed for cotton plantations, with labor supplied by thousands of enslaved African Americans.

Many had been transported by slave traders to the Deep South in a forced migration in the early part of the century, as the land was being developed.

During the American Civil War, more than three quarters of the adult white men in the county were serving in the Confederate Army by 1863.

In that year, a group of children petitioned the Confederate government to avoid drafting more white men, so they might serve as a home guard militia.

The petition claimed the militia was needed to guard against a potential slave uprising, since there were numerous cotton plantations with large numbers of enslaved African Americans.

While the county continued to rely on agriculture into the 20th century, the infestation of the boll weevil destroyed many cotton crops.

The northern boundary runs west from the state line along the 31°41' N parallel until reaching the Tombigbee River.

The Norfolk Southern Railroad runs north out of the Port of Mobile and along the eastern corridor of Washington County, providing transport of raw materials to several chemical and electrical plants situated along the Tombigbee River.

Factors contributing to this phenomenon include depressed economic opportunity within the county and the ongoing urbanization of the United States.

Its high schools include:[16] Like much of the Deep South, prior to the Civil Rights Movement of the 1960s, only white Washington County voters enjoyed the franchise, and they had long supported the Democratic Party in national, state and local elections.

After Congress passed civil rights legislation under the leadership of President Lyndon Johnson, in addition to legislation to support his Great Society policies, the county's conservative white electorate began to support Republican candidates in presidential elections.

With revival of their constitutional rights in voting, African Americans tended to align with the national Democratic Party.

That year the state's last Democratic governor, Don Siegelman, lost reelection to Republican Bob Riley.