 According to the U.S. Census Bureau, the county has a total area of , of which is land and (2.9%) is water.In recent years, average temperatures in the county seat of Galena have ranged from a low of in January to a high of in July, although a record low of was recorded in February 1996 and a record high of was recorded in August 1988.Average monthly precipitation ranged from in January to in June.