The Big Thicket is the name of a heavily forested area in Southeast Texas. While no exact boundaries exist, the area occupies much of Hardin, Liberty, Tyler, San Jacinto, and Polk Counties and is roughly bounded by the San Jacinto River, Neches River, and Pine Island Bayou. To the north, it blends into the larger Piney Woods terrestrial ecoregion of which it is a part. It has historically been the most dense forest region in what is now Texas, though logging in the 19th and 20th centuries dramatically reduced the forest concentration.
The Big Thicket has been described as one of the most biodiverse areas in the World outside of the tropics. The Big Thicket National Preserve was established in 1974 in an attempt to protect the many plant and animal species within. Big Thicket National Preserve, along with Big Cypress National Preserve in Florida, became the first national preserves in the United States National Park System when both were authorized by the United States Congress on October 11, 1974. Big Thicket was also designated as a Biosphere Reserve by UNESCO in 1981. The preserve consists of nine separate land units as well as six water corridors. Centered about Hardin County, the BTNP extends into parts of surrounding Jasper, Jefferson, Liberty, Orange, Polk, and Tyler counties.