Leitchfield is the county seat of Grayson County, Kentucky, United States. Leitchfield is a home rule-class city with a population of 6,404 as of th…Leitchfield is the county seat of Grayson County, Kentucky, United States. Leitchfield is a home rule-class city with a population of 6,404 as of the 2020 census. The town was named for Major David Leitch, an aide to Gen. George Washington and the original owner of much land in the county, including the town site, at the eastern end of his holdings. The city was formally incorporated by the state assembly in 1866.