Gillespie County is a county located on the Edwards Plateau in the U.S. state of Texas. As of the 2020 census, its population was 26,725. The county seat is Fredericksburg. It is located in the heart of the rural Texas Hill Country in Central Texas. Gillespie is named for Robert Addison Gillespie, a soldier in the Mexican–American War. It is known as the birthplace of 36th president of the United States of America Lyndon B. Johnson.