Oak Park, IL has a population of 51,989 and is the 778th largest city in the United States. The population density is 11,062 per sq mi which is 4876% higher than the Illinois average and 12110% higher than the national average. The median age in Oak Park is 39 which is approximately 5% higher than the Illinois average of 37. In Oak Park, 55% of the population over 15 years of age are married, 87% speak English and 5% speak Spanish. 60% of Oak Park residents were born in Illinois, 29% were born out of state, 1% were born outside of the United States and 10% were foreign born.