Rock City, IL has a population of 294 and is the 22,613th largest city in the United States. The population density is 1,927 per sq mi which is 767% higher than the Illinois average and 2027% higher than the national average. The median age in Rock City is 37 which is approximately 1% lower than the Illinois average of 37. In Rock City, 70% of the population over 15 years of age are married, 97% speak English and 2% speak Spanish. 73% of Rock City residents were born in Illinois, 25% were born out of state, 1% were born outside of the United States and 1% were foreign born.