 According to the U.S. Census Bureau, the county has a total area of , of which is land and (0.9%) is water.The county is bounded on the north by Sangamon River, and intersected by the south fork of that stream.In recent years, average temperatures in the county seat of Taylorville have ranged from a low of in January to a high of in July, although a record low of was recorded in January 1994 and a record high of was recorded in August 1988.