 According to the US Census Bureau, the county has a total area of , of which is land and (0.5%) is water.In recent years, average temperatures in the county seat of Sycamore have ranged from a low of in January to a high of in July, although a record low of was recorded in January 1985 and a record high of was recorded in August 1988.Average monthly precipitation ranged from in February to in June.