After this land was given away in 1815 by both Barren and Warren counties, the state of Kentucky named the land after former Kentucky Colonel John Allen. A lot of the history of this county was more than likely lost in the courthouse fire in 1902. The county size is 352 square miles with just over two percent of the county being made up of water. According to the 2018 census report, the county population is listed as 21,122 residents