High Quality Content by WIKIPEDIA articles! Blanco County is a county located on the Edwards Plateau in the U.S. state of Texas. As of 2010, the population is 10,497. Its county seat is Johnson City. Blanco is named for the Blanco River which traverses the county. The State of Texas formed Blanco County in 1858 from portions of Burnet, Comal, Gillespie and Hays Counties. The city of Blanco served as the county seat from 1858 to 1890, when it was moved to Johnson City.