Hill County is in north central Texas. Hillsboro, the county seat and largest city within the county, is at the junction of Interstate Highway 35 East and West, about fifty-five miles south of Fort Worth and thirty-five miles north of Waco. The county's center lies at 32°00' north latitude and 97°07' west longitude. Hill County comprises 1,012 square miles within the Blackland Prairie, Grand Prairie, and Eastern Cross Timbers regions. The county topography includes level plains and gently rolling hills at an elevation varying between 400 and 900 feet above sea level. The Nolan River, Mustang Creek, and Whiterock Creek drain into the Brazos River, which forms the county's western border. Streams in the eastern and northern parts of the county, such as Richland, Ash, and Bynum creeks, empty into the Trinity River basin. Flood controls and water supplies for the county are provided by Lake Whitney in the west, Navarro Mills Lake in the southeast, and Aquilla Lake in the southwest. Wells provide another source of water for many cities and farms in Hill County.
A small part of the northwestern portion of the county has Quaternary Period geology and includes a sandy clay loam subsoil. The dominant foundation of the county is from the Cretaceous Period and includes six subgroups. The Austin Chalk, part of the Balcones fault zone, is on a west-facing escarpment running northward to the Ellis county line from Abbott to an area northeast of Itasca. The soils are shallow and the grasses are short. The Taylor Marl in eastern Hill County yields a deep, waxy and clayey soil along the gently rolling prairies as they extend from Abbott to Brandon. The Eagleford formation is in the southern part of the county between Abbott and Aquilla and in the northern part between Covington and Files Valley. The black, waxy, clayey soil includes the rich rolling hills and farmland of Hillsboro and Itasca. Cotton, grain sorghum, and corn are the primary crops of the region and provide stability to the area economy. Natural vegetation includes bunch grasses such as buffalo grass, big bluestem, switchgrass, and indiangrass.
The Eastern Cross Timbers begins in the Woodbine formation that follows the reddish-brown sandy clay found along Aquilla Creek. Within this region, post oak, blackjack oak, live oak, and pecan trees provide a limited source of timber for the county. The Washita Group is a narrow belt of stony rolling hills composed of siltstone and limestone. The soil varies from shallow to deep concentrations of deposits rather than bedrock. The fossiliferous limestone of the Fredericksburg Group provides the western section of the county with dramatic limestone cliffs along the Brazos and Nolan rivers. The shallow soil yields short grasses, mesquite, and cacti. Bobcats, coyotes, white-tailed deer and gray foxes are among the animals found in Hill County.