Mechanicsburg, IL has a population of 623 and is the 18,196th largest city in the United States. The population density is 582 per sq mi which is 162% higher than the Illinois average and 542% higher than the national average. The median age in Mechanicsburg is 39 which is approximately 4% higher than the Illinois average of 37. In Mechanicsburg, 55% of the population over 15 years of age are married, 99% speak English and 0% speak Spanish. 87% of Mechanicsburg residents were born in Illinois, 13% were born out of state, 0% were born outside of the United States and 1% were foreign born.