Johnsburg, IL has a population of 6,285 and is the 5,587th largest city in the United States. The population density is 887 per sq mi which is 299% higher than the Illinois average and 879% higher than the national average. The median age in Johnsburg is 42 which is approximately 13% higher than the Illinois average of 37. In Johnsburg, 64% of the population over 15 years of age are married, 92% speak English and 4% speak Spanish. 76% of Johnsburg residents were born in Illinois, 17% were born out of state, 1% were born outside of the United States and 6% were foreign born.