McHenry, IL has a population of 26,631 and is the 1,621st largest city in the United States. The population density is 1,823 per sq mi which is 720% higher than the Illinois average and 1912% higher than the national average. The median age in McHenry is 40 which is approximately 6% higher than the Illinois average of 37. In McHenry, 61% of the population over 15 years of age are married, 87% speak English and 9% speak Spanish. 75% of McHenry residents were born in Illinois, 14% were born out of state, 1% were born outside of the United States and 9% were foreign born.