Most of the towns lie near the Sevier River in a fertile valley bordered on the west by the Pahvant Range and on the east by the Wasatch and Fish Lake plateaus.
National forests cover almost half of the land.
The area is seismically active, and a number of earthquakes have centered in the southern part of the county on the Sevier Fault. Many prehistoric Indian sites have been found. Fremont Culture sites continue to be found, especially during construction projects. Fremont State Park preserves artifacts from a recently uncovered prehistoric village. Jedediah S. Smith were among those who crossed the county before white settlement.