Oak Forest, IL has a population of 28,055 and is the 1,523rd largest city in the United States. The population density is 4,678 per sq mi which is 2004% higher than the Illinois average and 5063% higher than the national average. The median age in Oak Forest is 40 which is approximately 8% higher than the Illinois average of 37. In Oak Forest, 59% of the population over 15 years of age are married, 84% speak English and 6% speak Spanish. 81% of Oak Forest residents were born in Illinois, 9% were born out of state, 0% were born outside of the United States and 10% were foreign born.