According to the 2010 census, the county has a total area of , of which (or 99.53%) is land and (or 0.47%) is water. Elevations in the county range from above sea level where the Wabash River enters Vermillion County to in northeastern Prairie Township. The landscape consists mostly of flat or gently sloping moraine overlaying silty and loamy glacial till, except along the Wabash River where sand, gravel, sandstone and shale are exposed. Various forms of silt loam constitute most of the county's soil and are conducive to agriculture. Forests cover about 14% of the county, mainly around major waterways, and consist principally of deciduous hardwoods among which maple–beech and oak–hickory forests are the most common. The only coal mines in the county are located in the southeastern part of Steuben Township, near the Wabash River.