Allen county is in the Pennyrile region of Kentucky. The elevation in the county ranges from 445 to 966 feet above sea level.
In 2010 the county population was 19,956 in a land area of 344.34 square miles, an average of 58.0 people per square mile.
The equine population was 2,400 in the 2012 Kentucky Equine Survey.
Allen county was named for Colonel John Allen, member of the Kentucky Senate killed at the Battle of Frenchtown during the War of 1812.