[3] Washington County was initially settled by immigrants from Kentucky who moved northward out of that state in the early 1800s.

In the late 1800s there were (relatively) large numbers of immigrants who settled in Washington County, and by the early 1900s there were large numbers of first-generation immigrants still living in Washington County.

[6] On November 17, 2013, an EF4 tornado swept through the area, destroying homes and causing two fatalities.

As of the 2010 United States census, there were 14,716 people, 5,926 households, and 4,112 families residing in the county.

[13] In terms of ancestry, 53.6% were German, 14.0% were Polish, 13.1% were Irish, 7.7% were English, and 6.1% were American.

The only Democrat to win a majority of the county's ballots since the Civil War was Franklin D. Roosevelt in his 1932 landslide.

Historically, the county was dominated by organized labor and family farms.