Chillicothe, IL has a population of 6,169 and is the 5,653rd largest city in the United States. The population density is 1,203 per sq mi which is 441% higher than the Illinois average and 1228% higher than the national average. The median age in Chillicothe is 41 which is approximately 9% higher than the Illinois average of 37. In Chillicothe, 61% of the population over 15 years of age are married, 96% speak English and 1% speak Spanish. 85% of Chillicothe residents were born in Illinois, 14% were born out of state, 1% were born outside of the United States and 0% were foreign born.