Sour Lake is a city in Hardin County, Texas, United States. The population was 1,813 at the 2010 census. It was originally named "Sour Lake Springs", after the sulphurous spring water that flowed into the nearby lake; the sulphur was a sign of the crude oil that lay in proximity to local groundwater. 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".