sentences:  According to the U.S. Census Bureau, the county has a total area of , of which is land and (0.2%) is water.It is the fourth-largest county in Illinois by land area.In recent years, average temperatures in the county seat of Pontiac have ranged from a low of in January to a high of in July, although a record low of was recorded in January 1927 and a record high of was recorded in July 1936.