Mount Prospect, IL has a population of 54,552 and is the 737th largest city in the United States. The population density is 5,273 per sq mi which is 2272% higher than the Illinois average and 5720% higher than the national average. The median age in Mount Prospect is 40 which is approximately 6% higher than the Illinois average of 37. In Mount Prospect, 64% of the population over 15 years of age are married, 57% speak English and 15% speak Spanish. 58% of Mount Prospect residents were born in Illinois, 10% were born out of state, 1% were born outside of the United States and 31% were foreign born.