Gillespie County is a county located on the Edwards Plateau in the U.S. state of Texas. As of the 2010 census, its population was 24,837. The county seat is Fredericksburg. It is located in the heart of the Texas Hill Country. Gillespie is named for Robert Addison Gillespie, a soldier in the Mexican-American War.On December 15, 1847, a petition was submitted to create Gillespie County. In 1848, the legislature formed Gillespie County from Bexar and Travis Counties.