Johnson county is in the Eastern Coal Field region of Kentucky. The elevation in the county ranges from 550 to 1508 feet above sea level.
In 2010 the county population was 23,356 in a land area of 261.95 square miles, an average of 89.2 people per square mile.
The equine population was 700 in the 2012 Kentucky Equine Survey.
Johnson county was named for Richard Mentor Johnson, legislator and Vice President of the United States.
The Dawkins Line Rail Trail runs through the county.