Boulder Hill, IL has a population of 8,449 and is the 4,487th largest city in the United States. The population density is 5,794 per sq mi which is 2506% higher than the Illinois average and 6295% higher than the national average. The median age in Boulder Hill is 35 which is approximately 6% lower than the Illinois average of 37. In Boulder Hill, 61% of the population over 15 years of age are married, 80% speak English and 19% speak Spanish. 74% of Boulder Hill residents were born in Illinois, 17% were born out of state, 1% were born outside of the United States and 8% were foreign born.