Caldwell County is a county located in the U.S. state of Texas. As of the 2010 census, the population was 38,066. Its county seat is Lockhart. The county was founded in 1848 and was 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.