Trinity is at the intersection of State highways 19 and 94 and Farm roads 230, 356, and 1617, in southwestern Trinity County. It was founded in the winter of 1872–73 on land purchased from the New York and Texas Land Company. A previous settlement in the vicinity had been called Kayser's (Kyser's) Prairie. Millican's Chapel, built in the 1850s on nearby Bell's Creek, is the first known church in the area. The new town was a station on the Houston and Great Northern Railroad, which built through Trinity County in 1872. The community was originally called Trinity Station, after the Trinity River, two miles southwest. The name was later changed to Trinity City and finally to Trinity. When the H&GN bypassed Sumpter, the county seat, many residents of that community moved to Trinity, which became the county seat on May 20, 1873. Trinity then had two stores and five saloons. In 1874 the county seat was moved to Pennington, but Trinity remained a railroad center and the largest town in the county. By 1884 Trinity had four churches, a White and a Black school, several steam sawmills and cotton gins, and a population of 900. The population rose to 1,200 by 1890, but by 1896 it had declined to 500. Eleven houses burned in 1892. In 1900 Trinity had an opera house and an ice plant. In 1904 the population was 856. The community acquired its first light plant in 1906. Its first electricity was supplied by the Thompson Brothers Mill, which was established in 1907. In 1909 the business section was destroyed by fire, but the town rebuilt and incorporated in 1910. Trinity suffered another fire in 1915, and incorporated again the following year. By 1914 its population had climbed to 1,800, after which time it maintained a relatively slow and steady rate of growth. The White and Black schools were integrated in 1970. The population was 3,371 in 1988, 2,648 in 1990, 2,721 in 2000, and 2,697 in 2010..
Early settlers around Trinity engaged in agriculture and lumbering. Cotton growing peaked in the 1920s, when there were half a dozen gins in the area, but began to decline when prices fell in the latter part of the decade. Trinity was also one of the transportation nodes of the East Texas lumber industry. At one time it integrated 160 miles of railroad track and more than thirty sawmills. The first lumber mill near Trinity was the W. T. Carter Lumber Company, a mile west of town. The Thompson Brothers Mill was purchased by Sanderson-Ferguson interests in 1922 and renamed the Rock Creek Lumber Company, later the Texas Long Leaf Lumber Company. In 1952 Southland Paper Mills bought it and in 1955 liquidated it. A basket factory operated from 1926 to 1955. In the mid-1980s industrial interests in Trinity included steel and pulpwood manufacturing and one lumber company. A small field of oil, discovered north of town toward the end of the Great Depression, was still producing. The Texas Department of Corrections, which operated several facilities nearby, was also a factor in the town's economy. Trinity has many churches and civic organizations. Outdoor recreational facilities near Trinity include Lake Livingston and Davy Crockett and Sam Houston national forests.