Johnson County, created in 1858 from parts of Washington, Emanuel and Laurens counties, honors Herschel Vespasian Johnson, Georgia governor and Stephen Douglas' running mate in an unsuccessful bid against Abraham Lincoln in 1860. Wrightsville, the county seat, is thought to be named for John B. Wright, a pioneer resident.
This county's irregular southern boundary was an accommodation for a citizen so irate with his county commissioner that he prevailed on his legislators to separate his land from Johnson County. The Jefferson/Johnson county line follows the route of the Old Sunbury Road, one of the longest thoroughfares of its time. It was laid out in the 1790s.