Prairie du Rocher, IL has a population of 622 and is the 18,206th largest city in the United States. The population density is 1,089 per sq mi which is 390% higher than the Illinois average and 1102% higher than the national average. The median age in Prairie du Rocher is 34 which is approximately 9% lower than the Illinois average of 37. In Prairie du Rocher, 61% of the population over 15 years of age are married, 98% speak English and 0% speak Spanish. 79% of Prairie du Rocher residents were born in Illinois, 19% were born out of state, 0% were born outside of the United States and 1% were foreign born.