Buffalo Grove, IL has a population of 41,554 and is the 986th largest city in the United States. The population density is 4,382 per sq mi which is 1871% higher than the Illinois average and 4736% higher than the national average. The median age in Buffalo Grove is 42 which is approximately 13% higher than the Illinois average of 37. In Buffalo Grove, 69% of the population over 15 years of age are married, 63% speak English and 4% speak Spanish. 53% of Buffalo Grove residents were born in Illinois, 16% were born out of state, 1% were born outside of the United States and 31% were foreign born.