Forest Park, IL has a population of 14,137 and is the 2,966th largest city in the United States. The population density is 5,886 per sq mi which is 2548% higher than the Illinois average and 6397% higher than the national average. The median age in Forest Park is 39 which is approximately 4% higher than the Illinois average of 37. In Forest Park, 43% of the population over 15 years of age are married, 81% speak English and 6% speak Spanish. 62% of Forest Park residents were born in Illinois, 22% were born out of state, 2% were born outside of the United States and 14% were foreign born.