The Mission-Aransas Reserve is a large contiguous complex of wetland, terrestrial and marine environments named for the two river systems that flow into it. Located on the Texas Coastal Bend 30 miles northeast of Corpus Christi, the Reserve's 185,708 acres is representative of Western Gulf estuaries. Its extensive public and private lands include coastal prairie, oak motte, riparian freshwater and salt marsh habitats. This includes the private Fennessey Ranch with its more than 2,000 acres of uplands and 9 miles of river frontage. The Reserve's water areas consist of three large, open and shallow bays that support extensive tidal flats, seagrass beds, mangroves, and oyster reefs. The largest wetland habitat (24,400 acres) on the north side of the reserve is part of the Aransas National Wildlife Refuge and is the winter home to the critically endangered Whooping Crane.

The reserve is located in Aransas and Refugio counties, on the southeastern coast of Texas, approximately 30 miles northeast of Corpus Christi.