Knox County is named after Henry Knox, the first United States Secretary of War. The population of Knox County was 52,919 (based on 2010 census). According to the 2017 Census of Agriculture, there were 853 farms in Knox County, spanning 414,123 acres, with an average farm size of 485 acres. Knox County’s temperatures range from 13°F during January to 85°F during July. Average monthly precipitation ranges from 1.41" during January to 4.37" during July. If you're looking for land for sale in Knox County, IL, check out Land Pro LLC's current listings below. If there are no current listings in Knox County, take a look at land for sale in neighboring Henry County and Warren County. You can also view all the Illinois land offered for sale by Land Pro LLC.