Trinity County was established for judicial and other purposes on February 5, 1840. It was the first of sixteen such judicial counties to be established by the Texas legislature. It was originally known as the Northern Division of Liberty County and included most of the area of present Polk and eastern San Jacinto counties. The name was changed to Trinity County on December 7, 1841. Trinity County was abolished by a Texas Supreme Court decision, Stockton v. Montgomery (1842), which declared all the judicial counties unconstitutional. Present Trinity County was established in 1850.