Harristown, IL has a population of 1,240 and is the 13,840th largest city in the United States. The population density is 671 per sq mi which is 202% higher than the Illinois average and 641% higher than the national average. The median age in Harristown is 48 which is approximately 28% higher than the Illinois average of 37. In Harristown, 70% of the population over 15 years of age are married, 96% speak English and 0% speak Spanish. 82% of Harristown residents were born in Illinois, 15% were born out of state, 1% were born outside of the United States and 1% were foreign born.