Prospect Heights, IL has a population of 16,331 and is the 2,618th largest city in the United States. The population density is 3,839 per sq mi which is 1627% higher than the Illinois average and 4137% higher than the national average. The median age in Prospect Heights is 38 which is approximately 2% higher than the Illinois average of 37. In Prospect Heights, 64% of the population over 15 years of age are married, 43% speak English and 30% speak Spanish. 49% of Prospect Heights residents were born in Illinois, 9% were born out of state, 0% were born outside of the United States and 42% were foreign born.