Northbrook, IL has a population of 33,538 and is the 1,266th largest city in the United States. The population density is 2,534 per sq mi which is 1040% higher than the Illinois average and 2697% higher than the national average. The median age in Northbrook is 50 which is approximately 33% higher than the Illinois average of 37. In Northbrook, 74% of the population over 15 years of age are married, 78% speak English and 2% speak Spanish. 62% of Northbrook residents were born in Illinois, 19% were born out of state, 1% were born outside of the United States and 18% were foreign born.