Sour Lake, also known as Sour Lake Springs, is on State highways 105 and 326 and the Missouri Pacific line, twenty miles east of Hardin and eighteen miles southwest of Kountze in south central Hardin County. It was originally called Sour Lake Springs for the mineral springs that fed the nearby lake. It is the oldest extant town in Hardin County and was first settled around 1835, when Stephen Jackson received 4,428 acres at the site. Long before the advent of white settlers, however, Indians had made use of the mineral waters and of the pitch found around the oil seepages near the lakeshores. By 1850 these resources had made Sour Lake a health resort with good accommodations for healthseekers. Early entrepreneurs bottled the water and sold it; Sam Houston visited in the early 1860s, and an ex-slave named Bazile, who claimed to be an Indian, became known as "Dr. Mud" for his treatments. A Hardin County Sour Lake post office was established in 1866 and discontinued in 1876; a Jefferson County Sour Lake post office was established in 1877 and discontinued in 1880. But it was the Hardin County Sour Lake Spring post office, which operated under that name from 1879 to 1880, that became Sourlake in 1895 and that was still in operation in the early 1990s.
The town by 1885 had two general stores, two hotels, and a population of 150. By 1896 its population had declined to fifty with only a single hotel remaining. At that time the local school had twenty-eight pupils. Oil discoveries in July 1902, however, made Sour Lake a boomtown, where the population sometimes numbered 10,000, where peak oil production reached 50,000 barrels daily, and where as many as fifty-two saloons operated at one time. Half of the 150 wells at the oilfield were abandoned by 1903 because of extensive drilling. The community by 1906 had three schools with five teachers and 246 white pupils and one school with one teacher and thirty black pupils. By 1914 the Texas and New Orleans Railroad and the Beaumont, Sour Lake and Western Railway were serving a population of 2,800 at Sour Lake, which at that time also had four churches, a bank, and the Oil City Visitor newspaper. The Sour Lake oilfield produced about 90,000,000 barrels of oil up to 1948, when it was producing about 3,500 barrels daily and new drilling was still underway. The Texas Company (later known as Texaco) began at Sour Lake and in the early 1990s still owned the lake and the site of the former Sour Lake Springs Hotel. By 1925 the community's population was reported as 3,032, and fifty businesses were recorded after 1931. The number of residents declined to 1,504 in 1942, and the number of businesses to only 31 by 1947, but that year the town incorporated. Its population reached a high of 2,500 in 1976, and the number of businesses reached fifty-two in 1983. In 1990 the population of Sour Lake was recorded as 1,547, and forty businesses were reported. The population was 1,667 in 2000 and 1,813 in 2010. The community was noted for the Sour Lake Hardin County Fair.