Harrisburg, IL has a population of 9,418 and is the 4,123rd largest city in the United States. The population density is 1,433 per sq mi which is 544% higher than the Illinois average and 1481% higher than the national average. The median age in Harrisburg is 39 which is approximately 4% higher than the Illinois average of 37. In Harrisburg, 52% of the population over 15 years of age are married, 97% speak English and 2% speak Spanish. 76% of Harrisburg residents were born in Illinois, 21% were born out of state, 1% were born outside of the United States and 2% were foreign born.