Big Rock, IL has a population of 1,139 and is the 14,357th largest city in the United States. The population density is 264 per sq mi which is 19% higher than the Illinois average and 191% higher than the national average. The median age in Big Rock is 46 which is approximately 24% higher than the Illinois average of 37. In Big Rock, 72% of the population over 15 years of age are married, 96% speak English and 1% speak Spanish. 76% of Big Rock residents were born in Illinois, 23% were born out of state, 0% were born outside of the United States and 1% were foreign born.