Peru, IL has a population of 9,913 and is the 3,958th largest city in the United States. The population density is 1,049 per sq mi which is 372% higher than the Illinois average and 1058% higher than the national average. The median age in Peru is 46 which is approximately 22% higher than the Illinois average of 37. In Peru, 60% of the population over 15 years of age are married, 94% speak English and 4% speak Spanish. 86% of Peru residents were born in Illinois, 10% were born out of state, 0% were born outside of the United States and 3% were foreign born.