Jacksboro, the county seat and the largest town in the county, is sixty miles southeast of Wichita Falls and seventy miles northwest of Fort Worth. The county's center is at 98 10' west longitude and 33 12' north latitude.
Jack County is situated in the North Central Prairies region.
The land is undulating to hilly, with light-colored, loamy soils over very deep reddish clayey subsoils, shale, and sandstone. The county's 920 square miles is forested mainly by mesquite, live oak, blackjack oak, and post oak, with pecan, elm, walnut, and cottonwood trees along the waterways. The altitude increases from east to west and ranges from 800 feet to 1,350 feet. The West Fork of the Trinity River cuts across Jack County diagonally from northwest to southeast and provides the main drainage for the county. Among other creeks are East Rock, Howard, Lost, Crooked, the North Fork of Crooked, Little Cleveland, the West Fork of Keechi, Two Bush, and Henderson.