The Texas blackland prairies ecoregion covers an area of 19,400 sq mi, consisting of a main belt of 17,000 sq mi and two islands of tallgrass prairie grasslands southeast of the main blackland prairie belt; both the main belt and the islands extend northeast/southwest.
The main belt consists of oaklands and savannas and runs from just south of the Red River on the Texas-Oklahoma border through the Dallas–Fort Worth metropolitan area and into southwestern Texas. The Central forest-grasslands transition lies to the north and northwest, and the Edwards Plateau savanna and the Tamaulipan mezquital to the southwest.
The larger of the two islands is the Fayette Prairie, encompassing 6,600 sq mi, and the smaller is the San Antonio Prairie of 2,700 sq mi. The two islands are separated from the main belt by the oak woodlands of the East Central Texas forests, which surround the islands on all sides but the northeast, where the Fayette Prairie meets the East Texas Piney Woods.
Because of the soil and climate, this ecoregion is ideally suited to crop agriculture. This has led to most of the Blackland Prairie ecosystem being converted to crop production, leaving less than one percent remaining (and some groups estimate less than 0.5% to less than 0.1% remaining) and making the tallgrass the most-endangered large ecosystem in North America.