[2] It is located in the southern portion of Illinois known locally as "Little Egypt".

The county seal depicts the leaders of these two groups shaking hands.

[7] As of the 2010 United States Census, there were 17,808 people, 7,167 households, and 4,837 families residing in the county.

[17] In terms of ancestry, 23.0% were German, 12.6% were Irish, 9.4% were English, and 8.1% were American.

Like much of Southern Illinois, Union County has shifted toward the Republican Party over the past couple decades,[20] with the Republican candidate for president winning the county since 2000.