Caldwell County is a county located in the U.S. state of Texas. As of the 2020 census, its population was 45,883. Its county seat is Lockhart. The county was founded in 1848 and named after Mathew Caldwell, a ranger captain who fought in the Battle of Plum Creek against the Comanches and against Santa Anna's armies during the Texas Revolution. Caldwell was also a signer of the Texas Declaration of Independence. Caldwell County is part of the Greater Austin metropolitan area.