Johnson County is located in north central Texas on the southwestern edge of the Dallas-Fort Worth area. Cleburne, the county seat, is fifty-five miles southwest of downtown Dallas and twenty-nine miles south of downtown Fort Worth. Johnson County comprises 740 square miles with three geographical areas. The western half is a part of the Grand Prairie, where the predominant soil type is alkaline loam over limestone.
About one-third of the county is in the Eastern Cross Timbers, with acid soils that are both loamy with clay subsoil and sandy with loamy subsoils. The rest of the area to the east is Blackland Prairie, with deep clayey, alkaline soils. The Grand Prairie area supports grasses with cedar and mesquite and is inhabited by white-tailed deer, coyotes, rabbits, and squirrels. The Eastern Cross Timbers is a post oak savannah with some acreage of improved Bermuda grass and kleingrass. Cash crops of cotton, grain sorghum, and small grains are grown in the Blackland areas. In addition, pastures of kleingrass and Bermuda grass have been established. The primary natural resources in the county are sand and gravel.
The topography is level to gently sloping in the east and changes gradually to steep in some western parts of the county. Elevation ranges between 600 feet and 1,000 feet above sea level. The primary water sources are the Brazos and Nolan rivers. The Brazos flows along the southwestern border of Johnson County, and the Nolan runs north to south through the center of the county to join the Brazos. Secondary streams include Chambers, Buffalo, Mountain, Village, Mustang, Valley, and Walnut creeks. The upper portion of the Lake Whitney, on the Brazos, and Lake Pat Cleburne, on the Nolan, are the principal reservoirs. The average annual precipitation is thirty-three inches, and temperature averages range between a winter low of 35 degrees F and a summer high of 96 degrees. The grown season averages 233 days.