sentences:  The County was named for Pierre Menard, the first lieutenant governor of Illinois.According to the US Census Bureau, the county has an area of , of which is land and (0.3%) is water.In recent years, average temperatures in the county seat of Petersburg have ranged from a low of in January to a high of in July, although a record low of was recorded in February 1905 and a record high of was recorded in July 1954.