One of oldest towns in Montague County. Founded in 1850s, during great California Gold Rush, by E.S. and Ithane Singletary (Brothers) and John Hughes, who hoped to find gold here. The community they started became known as "Head of Elm" for its location at headwaters of Elm Fork of Trinity River. In 1858 Head of Elm ran—and lost—race for county seat. A post office opened here (at site of marker) in 1859, with John Womble, another pioneer, as postmaster. An early store and saloon were owned by Dominick Burns.
Next spurt of growth for town came with locating of Chisholm Cattle Trail through here about 1868. In 1871 village had a post office, blacksmith shop, and five stores. In 1872 I.H. Boggess (owner of the famous Stonewall Saloon) and Joe Howell bought 640 acres of land and laid out townsite, which Boggess named "Joe", for Howell. One story says he decided to add "Saint" because Joe was a staunch non-drinker; another version claims he added it to make the name longer.
In 1874 citizens built an all-faiths church and in 1876 a newspaper was established. Saint Jo was organized as a town in 1880; incorporated in 1886. Population has remained about 1,000 since that time and economy is still based on farming and ranching.