Oldham County was formed from Young and Bexar Territories, created August 21, 1876, and organized January 12, 1881. It was named in honor of Williamson Simpson Oldham (1813-1868), an Arkansas lawyer and jurist and a member of the Confederate Senate from Texas. Its county seat was Tascosa from 1881, and Vega has served as the county seat since 1915.