Hardin County is a county located in the U.S. state of Kentucky. Its county seat is at Elizabethtown. The county was formed in 1792.Hardin County is part of the Elizabethtown-Fort Knox, KY Metropolitan Statistical Area, as well as the Louisville/Jefferson County—Elizabethtown-Madison, KY-IN Combined Statistical Area. As of the 2010 census, the population was 105,543.