Willowbrook, IL has a population of 8,603 and is the 4,417th largest city in the United States. The population density is 3,198 per sq mi which is 1338% higher than the Illinois average and 3430% higher than the national average. The median age in Willowbrook is 45 which is approximately 20% higher than the Illinois average of 37. In Willowbrook, 59% of the population over 15 years of age are married, 71% speak English and 3% speak Spanish. 62% of Willowbrook residents were born in Illinois, 12% were born out of state, 0% were born outside of the United States and 26% were foreign born.