Lockhart is a city and the county seat of Caldwell County, Texas, United States. According to the 2020 census, its population was 14,379. Th…Lockhart is a city and the county seat of Caldwell County, Texas, United States. According to the 2020 census, its population was 14,379. The city of Lockhart is named after Byrd Lockhart, an assistant surveyor of Green DeWitt and reportedly the first Anglo to set foot in Caldwell County. Lockhart was the site of a victory of the Texans over the Comanche, at the Battle of Plum Creek in 1840. Lockhart was originally called "Plum Creek", but the name was later changed to Lockhart.