Sour Lake is a city in Hardin County, Texas, United States. The population was 1,773 at the 2020 census. It was originally named "Sour Lake Springs", after the sulphurous spring water that flowed into the nearby lake. The city is part of the Beaumont–Port Arthur Metropolitan Statistical Area. Sour Lake is the oldest surviving town in Hardin County. It is called by some the "Gateway to the Big Thicket".